I use BCW Monster 5000 Boxes originally designed to hold trading cards. They are easily modified to fit most all O-Gauge equipment. Engines, cars, parts etc. I also affix a stick on Index Card Holder that hold a 3"x5" index card. The JUVALE Index Card Holders are procured from Amazon. The Index Cards are used to list the contents of the BCW box. If the contents of the box changes the Index Card can be replaced easily with a new card with the new list. Good system to help keep track of everything including Junk items. The boxes are strong enough and stable enough to be stacked 8+ high.
Happens to most including moi. Have many in large blue plastic storage bins or their original tattered boxes under train table and many engines on shelves do we sometimes have to much for 1 person - you bet. ; )
But its so much fun !