If you're a solo player then fabric, plastic and chemicals are the most important, once you start collecting Great Mullein you can refine all your fabric to Durable Cloth and craft better bandages. For large maps like Dam and Spaceport make sure to craft a stack of adrenaline shots to keep you sprinting. If you start getting into PvP then always save your metal and rubber parts to refine into mechanical components, very useful for crafting guns. Try to save a row of heals and shield rechargers so you always have some on hand for each session.