Items come into two different groups, Objective Items, Standard Items and Scenery Items. Scenery Items have almost little to no-effect in-game despite being in abundance.
Objective Items, are items that play towards an objective, these can be cards or keys of some sore or parts of a machine which must be found.
Standard Items, are items that help players during gameplay, typically doing actions such as restoring health and adding armoured protection.
Regular props, are objects with little to no effect on gameplay. They are often used as a source for barricades.