There was a guy I saw at a range in Miami, his range bag was a vertical hard sided tool box, mounted on a roller cart like the old lady shopping carts. Full of spares and tools.
I had assembled my first AR and was having light strikes. He was a couple lanes down but offered to help. Diagnosed a backward hammer spring. Popped it all out, reinstalled, also noticed I didn’t have a spring in the front takedown pin. (Sprung while assembling of course!) so he popped the correct one in as well.