I usually get a hold of 2 weapons which use the most common soviet round, you find those on just about every corpse, and leave everything else behind, unless it's something extraordinary. In addition to having lots of ammo to be found they are also cheap to repair, and not so different from the more expensive guns once upgraded. I much prefer being able to run for extended periods over heavy armour and weapons.
I just recently finished the prequel, Call of Pripyat. The weapons get insanely powerful and accurate once upgraded to tier 3. Unfortunately once it becomes available the game is pretty much over. I spent hours hamstering enough money to upgrade everything, go back to Pripyat and it's literally over in 15 mins. I don't think the developers really understood how people react and play the game when they finally get access to the final upgrades. Big disappointment.