@copycat I thought the same, but if you print "Bierkiste-Batterien-Boden" and glue it to the bottom, they cannot slide off anymore. 🙂
Alternatively, I've used these little feet: https://www.printables.com/de/model/475141-legs-for-beer-crate/ , which also work nicely! (edited)
Stackable, but doesn't "lock" to each other like the real crates and it can slide off.
Perfect for leftover filament. (edited)