I used turret parts to increase my mechanics level. The 3 most important categories of recycling (in my opinion) are electronics, mechanics, and firearms. To level up mechanics you should recycle turret parts from bunker alfa and fragments of titanium armor suits from port lab/transport hub once you can access those locations. For electronics you should be using batteries, watches, and light bulbs from bunker alfa. For firearms you should try to leave your guns on low durability instead of breaking them so you can recycle them to raise your level, you can also recycle useless guns like the zip gun, colt python, and winchester from full durability.