Just wrote this up so people can see what the items do from the Workshop page - please tell me if the information is incorrect.

The developers made almost everything configurable, so you can tweak whatever effect to go on whatever item, with the values you want.

Numbers surrounded by [brackets] are configurable values.

AI2: Heals [4] health per second for [30] Seconds
Bandage: Immediately stops bleeding
Stimulator: Multiplies movement speed to [130]% of its original value (0.8 speed becomes 1.04 speed)
Infantry Medkit: Immediately heals for [50] health.
Analgin: Speeds up the decay of suppression effects (screen will darken and aim will become unstable when shots / explosions hit you or land nearby) by [10] times for [10] seconds.
Revidol: Revives a dead soldier (works on enemies)

The keybind to open the inventory is [k] by default.
Within the inventory menu, a visual icon shows what the item's effects are. (Blood droplets = stop bleed)