This is an organizational problem, and one you can fix if you make a few simple changes.

You need each student to get a mesh or drawstring bag like the extremely cheap backpacks handed out all over or this one..

Write each student's name on the bag, attach the bag to the hanger with their uniform.

They should be traveling to and from the game in uniform. Full uniform when departing, full uniform when arriving. That fixes the "leaves things behind" problem.

These are problems you can solve if you institute standards and cultural expectations.