Hi and welcome to POTN.
You will probably be able to find the 6D in kit with a 24-105/4L. That's a good way to buy because effectively the lens is nicely discounted.
However, just so you know, there's an even cheaper alternative. The Canon EF 28-135 IS has been sold a lot in kit with various models for a number of years, so there are a ton of them around on the used market at steep discounts. The image quality, IS, close focusing ability and focus speed (both are USM) are all virtually the same as the 24-105. The 28-135 is slightly soft racked all the way out at 135 (stop it down to f8 to sharpen it up), but of course the 24-105 doesn't go that long at all. The 24-105 has more vignetting at the wide end, but of course the 28-135 doesn't go quite as wide.
Besides the slight difference in the focal lengths, the main differences are that the 28-135 is a variable aperture lens (f3.5-5.6) and the L-series lens is better built and better sealed. But since it's often possible to find at 1/4 or even 1/5 the price, takes every bit as good images and performs just as well, IMO the 28-135 is one of the better bargains out there. Especially if you plan to get some prime lenses to complement the "walkaround" zoom with, anyway.
That said, the older 24/2.8 and 35/2 are not USM lenses. They both have decent image quality, but they use older micro motor focus drive which is a little noisier, slower and less accurate than the USM of the newer IS versions, which also offer improved IQ. Now, on wider lenses like these the micro motor isn't too big a deal, since they only need to move their focusing group a short distance to achieve focus. But USM also allows for "Full Time Manual" (FTM) focus override. With the micro motor lenses, you must turn off AF at the switch, before manually focusing them. Failing to do so, you'll break the AF mechanism. USM lenses, on the other hand, can be manually overridden at any time, without turing off the AF. The skinny focusing rings of the older 24/2.8 and 35/2 don't encourage manual focus, either. Plus the build quality of those older primes, while a couple notches above that of the most entry level lenses like the 50/1.8 II, isn't quite as good as the USM lenses. For example, the older 24/2.8 and 35/2 both have metal bayonet mounts and distance scales, while the 50/1.8 II lacks a scale and uses a plastic bayonet mount. All four lenses are a bit plasticky in construction (isn't everything these days?), but if you compare them side by side you'll find the newer IS versions simply "feel" a bit better built, particularly the 35/2 IS.
So, in other words, there's a lot more to the newer, IS versions than just the stabilization. They are all around better built, better IQ, better focusing lenses... plus the IS (which personally I feel is less-than-necessary on a lens in these focal lengths). Of course, they cost more. And so do their accessories. I'm not sure about Nikon (all my Nikkors are vintage), but many Canon lenses don't include the lens hood. Only L-series include it. The 24/2.8 IS and 35/2. IS are not L-series, and their separately sold matching lens hoods are rather pricey at $54 each, the last I looked. There are considerably cheaper, but just as effective third party clones of the hood for the 24/2.8 IS available (eBay). But they haven't yet begun offering one for the more recently introduced 35/2 IS. I'm sure one will be offered soon, though.