Organisation systems fail at the same place: the objects that do not belong to a category. Keys. A card. Two screws. The little tool that came with something. None of them has a drawer, and each of them individually is too small to justify one.
A tray does not solve this. It contains it.
The size question
Too small and it overflows and stops being a boundary. Too large and it becomes a second desk surface and collects paper, which was never the point. A hundred and sixty by a hundred and ten is about right for oddments; anything bigger is a different object with a different job.
The floor matters
A metal tray with a metal floor is loud, and it scratches watch glass and phone backs. A felt floor costs almost nothing and changes the object from something you drop things into carefully to something you drop things into.
