There are four tiers of first aide, Tier 0, 1, 2 and 3. Tier zero is whatever you find out in the wild outside any medkits. Tier one is a simple first aide kit, fit to keep one person in tiptop shape, while Tier two is enough for a small group, they are medical satchels and they're a little harder to find. Tier three is a Trauma Bag and consists of enough medical supplies to keep an entire squad alive!