When I went to do Nimble's quest for armor, that ugly looking dog thing from the tunnel came out and had a tail once I killed it. Just head towards the bandit camp (very first thing to do pretty much) but go around and behind it, then keep going a little more. There's some packs of dogs then that ugly mofo from the tunnel.
I was able to get better weapons pretty quickly. I stuck around the first Cordon area for too long probably, but I was having fun doing whatever. After you originally kill the bandits (1st mission), go back and get your reward, then go around and do whatever. I went to the NW (I think) where there is a bunch of anomalies and the tunnel to enter to get across the tracks except didn't do through the tunnel, collected artifacts and anything around, then went back to the bandit camp. There was several new bandits there with AK74 and whatnot. The bandits there generally come back fairly often. So before I went to the military checkpoint to pay to get across, I already had the better pistol, AK74, and Viper 5 I think.
Just loot all the bodies and crates you find. I've always ended up with too much weapons, ammo, aid kits, etc. Of course on a harder difficulty you might not.