"That's what a Vac-U-Form can do!"[1]

TechShop used to have a medium sized vacuum forming machine, but it was lost in one of their moves. Those are useful for tool trays. Lay down all the tools for some kit, vacuum-form a tray, and put the tray in a case for the kit. Often used in aerospace, where you want to make sure nobody left a wrench inside the engine or fuel tank.

[1] https://www.youtube.com/watch?v=lCvgvWiZNe8

That sounds a million times easier than modeling gridfinity trays.

reminds me of a certain car trunk scene in Simon Pegg's "Kill Me Three Times" (although it used a custom foam insert and not vacuum-formed plastic)