the two-lens kit.
I've long been a photographer -- back to my Jr. High days (and good enough at it that I did the photography for much of the yearbook sports during that time.) Had my own darkroom gear (B&W; I wasn't rich) at that time as well and bought Tri-X by the big roll to defray costs, loading my own 35mm cartridges.
Digital came "of age" in real terms in the 2000s; before that you could get it, but it wasn't worth it. It still has a dynamic range penalty, but that has narrowed a lot over the years. dSLRs were my thing, but there's a damnable element to this, especially with full-frame (as with 35mm, which is the same size) in that lenses, especially good ones, are both frightfully expensive and heavy because good glass in large amounts counts both money and mass -- there's simply no way around it.
In addition the general rule has never changed in that primes (one focal length) tend to be faster (larger maximum f/stop) and better, since nothing internal has to move fore and aft except for focus, but they're expensive and of course you need a lot of them. Zooms tend to cost more (more elements in them), have more moving parts and can't be optimized over the whole range, tend to have narrower apertures and thus all things being equal the maximum resolving power (image quality) tends to be less. You can defray some of that -- but not all -- with application of money.
This leads to a conundrum: What are you going to point the camera at today, do you know this in advance, and what do you carry so you have appropriate choices in depth-of-field, light gathering and magnification -- and what compromises will you make in each?
The "holy grail" is to have one lens that covers at all on a given camera. Forget it. Not even Jesus can pull that one off. And until fairly recently it was basically impossible to cover even 80 or 90% of it with two lenses. Thus you were stuck with three, four or more -- and had to carry them if it was possible you'd run into a need and they're both big and heavy, never mind expensive.
Well, to a large degree this is now a solved problem. No, it is not every case; specifically, moving subjects (e.g. sports or moving wildlife) in limited light remains a problem, as does extreme wide-angle stuff. Nor can you solve the money problem; sorry, good glass has always been expensive, the better it is the more-stupid expensive it is, especially when you want it in longer lengths at reasonable apertures. But -- in terms of "I need five" well, maybe not.
Maybe now its two for the 85% or 90% of things you want to do. Really.
I'm speaking of the Canon RF full-frame line with the trade-off point in the body area being the R6 MkII. Is there better and faster? Probably, but its at the margin; that body will do most things and it can also shoot 4k video very competently (including at high bit rates) in addition to stills. It, like all mirrorless cameras, takes getting used to if you're coming from a SLR of any sort because the viewfinder is in fact electronic so what you see in there is a television image rather than the image. This, however, means the camera can superimpose data on the image which can be very helpful -- but can also frustrate until you learn how to set it up (and no, what you wanted in terms of "back button focus" and such on an SLR is not what you want on these -- trust me on this, you will have to relearn how you want the camera set up and until you do you're going to get really, really frustrated and swear a lot!) Incidentally a ~$100 adapter (just the flange difference and pin pass-through) allows the RF bodies to work w/o limitation with all the older EF glass, so if you own that glass already, particularly for special circumstances that's a huge advantage.
On to the glass. Two lenses: the RF 24-105 L in either the f/4 or f/2.8 (bring money and mass) versions. The f/4 is half the price, uses a standard 77mm filter (e.g. UV filter, polarizer, etc.) where the f/2.8 uses a more-expensive 82mm and is double the mass as well as double the money. Both are excellent and if you need the lower-light capability for moving subjects (more on that in a minute) or want the better-bokeh from the faster lens while being willing to put up with the extra pound and a half of glass then bring the money, and lots of it.
The second is the RF-100-500 (!!) f/4.6-7.1 L. NOT cheap, but hear me out. Yes, I know, you say that aperture is a problem. It is if the subject is moving and light is low. Thus you can't get beyond about 90% of the use cases outdoors, and for some people -- especially if you shoot indoor sports, this is just not going to work and you have to bring even more money and mass for those situations since you need a wider aperture. But if that doesn't apply then yeah, this does the job out to many wildlife shooting circumstances. Not all, but many. It too takes a 77mm filter, comes with a very nice hood (as does the 24-105, both of which can be put on backward for storage or if you don't need them at the moment), and while it is heavy (3lbs) its not stupid heavy. It also comes with a foot that you probably want to put an ARCA plate on for your ballhead as it balances better there than on the camera but this lens is surprisingly hand-holdable in many circumstances as its stabilizer is astoundingly good. At 500mm shots down in the 1/30th-1/60th of a second range can be sharp handheld with no motion blur at all provided the subject is not moving. The newer RF bodies are a game-changer in another respect in that their autofocus performance at these narrower apertures is outstanding where you'd otherwise expect it to be marginal -- or refuse to lock at all. The 100-500mm has dual autofocus servos in it which undoubtedly helps a lot; playing around with it pointing it at squirrels and such in the back yard and beyond it grabs focus instantly and very, very reliably. I though my older Tamron was really good both on my 5d3 and R6 MkII but this lens, in combination with the RF body (it won't mount on the 5d3 of course as the flange distance is wrong) is in a whole different league.
Thus two lenses, one full-frame body and you have coverage from reasonable wide-angle all the way out to the "super telephoto" range -- provided you have decent light and can afford the check.
This does present one problem however -- my "small" pack that used to hold a dSLR with a 24-105L, my 70-200mm f/4L and a few accessories (extra battery, charging dock for the batteries on USB, couple of extra cards, etc.) is just a bit too small to hold the camera and the 100-500mm. My medium Ape Case easily does the job and can also take my X1 Carbon in the pocket along with a bunch of accessories (including my Sennheiser mic kit for video) so it probably winds up being "the obvious choice" but this does mean that my "smaller and lighter" option is gone until I can find a replacement sling case -- slightly larger, as I need just a bit more volume. The problem is on the width side, not length, as the 100-500mm is a bit larger in diameter and simply won't go with any reasonable configuration.
Ah well, I'll figure it out -- and the Ape Case (which incidentally I highly recommend except for the fact that they very-much advertise that there's a camera in there, so you can't leave it unguarded ever or someone will take a five-finger discount) will do for the time being. The medium one incidentally clears under-seat even on small plane flights where the large (which I also own) does not, so that gets your high-value camera and computer gear in the plane with you in virtually every circumstance if you travel, and there's enough room to get a change of clothes and such in the event your checked bag goes missing for a day.
In any event for those of you who are looking to do the same or more with less this is a decent set of options and one that, a few years ago, was simply not possible. There were 100-400mm zooms from Canon before and of course the Tamron 150-600mm (which I shot both solar eclipses with and is an awesome piece of kit, especially for the money) but its big, its heavy, the corners are not as good as I'd like especially at 600mm (there are always compromises when the lens doesn't cost $12,000!) and it is definitely not conducive to hauling it around unless you strongly suspect or know you're going to need it and it really wants at least a monopod for support simply due to its size and mass -- handholding that beast is not fun and flat-out forget it in anything other than excellent light conditions.
Incidentally if you need more reach rather than buy the 1.4x extender (which you can do) or wildly increase cost by buying a longer prime with a five-digit price tag I would seriously consider adding the R7 body to your kit instead. Why? Well, you do give up some amount of light gathering as its an APS-C sensor (smaller and thus more-dense) but you get 1.6x focal-length extension on all the lenses so that 100-500 becomes a 160-800mm lens while maintaining its f/7.1 aperture. Plus you have a backup body (albeit in APS-C) if your primary pukes and its a hell of a lot cheaper than buying longer prime glass and unlike the 1.4x extender there is no image quality loss. You could also choose to have "instant range" capacity, if that's your thing by mounting the 24-105L on the R6ii and the 100-500mm on the R7; now its "grab one" instantly provided you can rig your carry bag to work with that. Incidentally if you shoot video the R7 reads out considerably slower than the R6 MkII and the light-gathering penalty becomes more-severe with video in many instances so if shooting in 4k or available light you're much more-likely to run into motion artifacts (especially if panning) and IQ degradation with the R7 so for video the R6MkII is the far better choice.
IMHO this is a much more "social" setup in all respects than the older dSLR pro-level bodies plus appropriate lenses (e.g. 5d3, 5d4, etc.) and makes hand-holding very reasonable in circumstances where it formerly was not. It isn't cheap but then again quality never is.
Recommended.