Glue

On paper, glue has exactly one job: duct tape, listed as one glue and five cloth at a Level 3 workbench. But the game files say duct tape cannot be crafted at all, and it goes into nothing anyway, so in practice glue has no use, and few components are more minor than this one.

No recipe makes glue, so any you hold came out of loot. The only other way back is recycling duct tape, and that returns glue only some of the time. Glue itself shows no recycler output at all.

A typical moment: you open a crate by the road and a tube of glue sits next to a couple of gears. Take the gears, leave the glue. If your base boxes are cramped, it is one of the first things to go, and the useful parts are in the components list.