I added spots for you to put 4 8mm x 3mm and 4 10mm x 2mm magnets to hold the lid in place better.

4 - 8mm x 3mm Magnets I used these - DIYMAG 150Pcs Small Magnets, 8x3mm Tiny Refrigerator Magnets, Neodymium Rare Earth Magnets for Office, Whiteboard, Kitchen, Durable Teacher Magnets for Crafts, Dry Erase Magnets, Mini Button Magnets: Amazon.com: Industrial & Scientific

4 - 10mm x 2mm Magnets I used these - FINDMAG 100 Pcs Small Magnets, Rare Earth Magnets, 10x2mm Mini Magnets, Neodynium Fridge Magnets, Tiny Nail Clipper Magnets, Round Magnets for Nail, Whiteboard, Refrigerator, DIY Crafts: Amazon.com: Industrial & Scientific

and a glue of your choice.

I attached the magnets with hot glue myself.

This will fill a 100-card double-sleeved commander/EDH deck and 3 D20s/Spindown life counters.