Really Useful Boxes are great ... just occasionally I have something that doesn't quite fit into one. This was particularly annoying because everything else that goes with it does fit into the 9 litre boxes. The solution: make my own.
Critically, the things that go into this box are longer than would normally fit - so this version has thin plywood ends. It is also shallower than the 9 litre plastic version - but deeper than the 4 litre that has the same footprint. Both the lid and the base have extra bits glued on so they don't slide about when stacked with their plastic cousins.