Always loot everywhere. You see a locker, file cabinet, desk, body--anything--at least search it first. Rarely, you'll find something with some substance like weapons, but what you're mainly looking for is chems and ammo. Chems are pretty light weight and having a full stock makes you invincible for most of the battles ahead. But the real gems are the ammunition. I cannot stress this enough, TAKE ALL THE AMMO YOU COME BY. ALL OF IT. Ammo has no weight AT ALL, so even if you don't use it, it will accumulate over time. Then just sell whatever you don't use then next time you see a shop. Essentially, the every shop owner you come by will run out of caps to give you by the time you're through with them, making you the richest bastard in the wastes.