You are limited to what your mercenaries bring with them and what you find on the island, on the bodies of dead enemies, buried in the ground, or stashed away in crates. Your mercenaries cannot carry an unlimited number of items, so you're going to have to make some tough decisions about what items you want to carry with you and what items you can leave behind. You've always got to keep an eye on your inventory because most items are going to be in much scarcer supply than you'd like. Think twice before tossing that last grenade because you might need it later and not have one. You've also got to maintain and improve your weapons, which is why you need a mercenary with good mechanical skills.
Weapons deteriorate over time in the harsh jungle climate.
Weapons which are in poor shape have a bad habit of jamming at the most inopportune time. In addition, some items can be combined to increase the accuracy and power of a weapon. Other items can be combined to create various types of explosives. The most satisfying elements of the game are the RPG aspects. Enormous care was taken in the creating of each mercenary to give them distinct personalities, strengths, and weaknesses.