Either:
The best camouflage I can lay my hands on.
The best body armor/flak jacket I can lay my hands on.
The best entrenching tool/shovel I can lay my hands on.
The idea here is that they won't intentionally shoot you if they can't FIND you.
WWII:
M1911A1 with some feed ramp and ejector port tuning for absolute assured reliability.
Thompson SMG, almost any variant,(for ammo commonality with the .45)
At least 200 rounds in .45 for both guns,
mostly loaded in lots of spare mags including drums for the Thompson.
M1 Garand for long range work
Yeah, it'd be a heavy gun load for one man but I'd rather be a little tired and well armed than travel lightly and not have the weapons I need.
Consultation with experienced battle veterans of the time would give me further guidance as to what's actually useful and what's not.
I wouldn't bother with the niceties like books, candy, lipstick, etc. because I'm not chasing tail and with a gun, I can get what I want anyway. When an armed man asks if you can spare some food, the answer is YES! Especially if he's trying to liberate your country!
Future:
Go with the classics! M1911A1, Thompson, Garand!
Freak EVERYBODY out!
But seriously, I WOULD choose an M1911A1, and I would choose both short and long range rifles. An M16 (possibly an SMG) and an HK 91 or something like that.
CJ