Bolt? .308/7.62 NATO Savage.
“Assault Gun”?. AK in7.62x39
Lever? Marlin 336 in 30-30, using Hornady Leverevolution Ammo.
I agree with this list, but might add the Mini-14 for .223 or Mini-30 for the 7.62x39. I have both and love both. I also thought the 30-30 might do well in bad times. I have a Ruger M70 in 30.06 for the reach out and touch shots. I have a 7 mag. but ammo may not be everywhere and I don't see enough difference in the 30.06 to worry about. I had a Savage 30.06 but got rid of it for reliability reasons.
Much of this depends on what the writer will do with it. Just as a general gun I would stick with .223 merely for all around long shots and ammo is everywhere.