Explosives

You make explosives so you can make C4 and rockets. Nothing else in a normal wipe asks for them in any number, and those two swallow plenty: a single C4 takes twenty, a rocket ten on top of its own gun powder.

Two things gate them. The blueprint needs a Level 3 workbench and a hefty chunk of scrap to research, so solo players often run their first raids on satchels and beancans instead. And each craft gives you exactly one, so a raid of any size means a long queue at the bench.

Keep the finished stack in one box deep in the core of the base. A box full of explosives is exactly what raiders hope to find, and losing it costs you days of sulfur farming.