You eat a sausage or loaf of bread every now and then. Not really a major element. You have medpacks and bandages, but Metro has morphine syringes.
You can carry around expensive special weapons and trade them down for "inferior" weapons at a trader to get more MGBs than you'll ever need. It's really easy to do in the beginning of the game. You can get an easy electro-driver (worth a crapton of boolits) at the first group of bandits you encounter with Bourbon, trade it for the crappy shotgun at the next trader you encounter, and then replace it with the Hellsing you find later. Congratulations, you now have way more MGBs than you'll ever need (even on Ranger Hardcore, which ironically is a LOT easier than regular Hardcore) and you also have arguably the best special weapon.STALKER's Rubles are hard to obtain? O.o
It's not emulating when Rubles are quite literally just currency without the potential use as being an ammo source.
You can repeatedly kill people, sell their equipment, and make money (ruble) that way. It is tedious, but it isn't hard to find.
Military grade bullets are limited, period. You shoot it, it's gone forever, there is no method to farm it or anything.
Catches on rather quickly. Should have it record and see how fast it goes up in time lapse.
Keeping a good-condition high end rifle or suit of armor in unmodded STALKER becomes really expensive really fast, especially for the rarer things like the Colt M4A1 knock-off.