Stock Up on Items
Scattered around missions are Logisticians (marked on your map as white chests). These special soldiers exist for the sole purpose of stocking up your items. When you first start a mission, you’ll have a few of each item available to you (not counting canisters, you only get one of those for some reason). Still, those are finite, and if you find yourself relying on items as part of your play style, then you’re going to want to always make sure you have some.
Locate these Logisticians as you traverse the battlefield and interact with them by pressing Circle/B. They’ll give you one of each item in your inventory, unless it’s maxed out of course. You can also find stray items scattered around the field that are dropped by killed soldiers. These will pop up on your map with an icon representing what they are.
