The main idea is you have two rifles that you grab most of the time that you know inside and out. Or it can be one as far as that goes. These two should always be ready to go hunting at any time. Should always have plenty of components/ammo on hand for them at all times.
A custom barrel 1:7 or 8 twist .243 Win and .308 Win in no more than a 7.5lb all up rifle 20-22" barrel. Nice lightish, fast handling, easy to shoot rifles. Present situation excluded, components and ammo were common and easy to get plus there is more than a little commonality between the two for components. If you can't kill a pronghorn, goats, sheep, and deer with a .243 or elk/moose with a .308, it isn't a rifle/cartridge issue is all I'm going to say.
If you're goint to use factory rifles 6mm Creedmoor and .308 Win for a lot of the same reasons above.