Since somebody got to the Hammer before I did
let's add some books with minor tidbits rather than full blown "Post disaster":
"Footfall" Aliens attacking earth by throwing rocks from orbit. Some nice scenes describing a post-strike trip through the US complete with a "Survivalist" group.
"SS GB" by Len Dighton shows a world where "Sealion" went off and the survivors have to life in an oppressive society (Maybe useful if you start "Slaves of New America"
"War World:Invasion" is a short story anthology about a planet trying to survive with most of it's infrastructure in ruins and the evil attackes (with higher tech gear) conquering it. Some stories are useful for "Survivors trip" scenarios
As for "Steiner/The Iron Cross" (Books even better) try out "Hunde wollt ihr ewig leben" (Stalingrad battle, 50s movie, might be out under "Dogs do you want to live forever" or so) and "08/15" by Kirst (WWII, the author is one of the soldiers, most likely "Asch"). At least gives you a lot of soldier archetypes. Ones that you can meet IRL
"Tour of Duty" Don't know how realistic it is but it makes for great clichees (A bubbly but green Lt's still called a "Myron" in our games)
The "Legend of the Aldenaata" cycle by Ringo has some nice ideas of desolate America with a strong government
War in 2020 shows a broken down UdSSR and (nice twist) the evil japanese hords. Story deals with a US unit helping out but the descriptions around that are interesting
For soldiering you might try "Protect and Defend"
Oh, and "The 10000" about the greek mercenaries on their way home. Refugees and soldiers marching home are always the same wether they use slings&lances or M16s and AKs
If you're into "Empire building" and "marry the princess" you might try "Janissarians"
And yes, Clancy is an amateur that makes "Screaming" errors (German Landwehr i.e) but a nice reading for a game.
Michael