When carrying the boxes around I was always worried about dropping the stuff in them. I created these lids so that that will not happen.
There are two types, plain and with grid. The plain ones are just lids but I wanted to be able to stack other bins on top so I added the gridfinity grid to the top of them.
They snap on and off any bin with the stacking lip on it, if there is no stacking lid they will not be able to snap on.