My van's not as bad as it was years ago, I've had to lean it out AND find room for more diverse things. It used to be we were told to limit what we stocked for repair parts. Take pictures and order what was needed for a return trip. If I ordered a stem for my van the parts person would ask permission from a manager before ordering it. Our shop Sloan kit was well stocked and none of us had Sloan parts on the vans. Maybe a half dozen shower valve cartridges. It was brutal. I hated subjecting customers to a second, unnecessary trip for a Moen 1200 or a Symmons TA-10. Motto was "get eyes on it" and figure out what we need to come back.
A couple years ago we lost our two other good service guys leaving only me. Calls went up due to covid and the urban flight. The new guys they pulled off newcon were dysmal. This left me being sent to all sorts of situations where we didn't know what I'd find, and we didn't want a second trip because we were so strapped for man hours. I am now our only real service plumber and have been for quite some time. The past several years I have been able to order ANYTHING. A couple weeks ago I ordered a Wal-Rich spud buddy mostly just to see if I could! It was special order and they had it delivered 2 day shipping without even asking me!
Since things changed I stock pretty much everything. I go through the van regularly looking for overstock and tools I don't use. I keep softener parts, Sloan parts, several sump pumps, all sorts of well pump parts like checks, ccvs, foot valves, control boxes, insert fittings, sweat fittings for pressure up to 1-1/4", a few 1-1/2" copper dwv parts, 5 float switches(instead of 2), electrical parts like jboxes, switches, romex, bx. And all of that is on top of the usual pipe and fittings I carried before and all of the snaking equipment.