I'd venture a few guesses:
The large flat one probably for putting small parts there that you may have taken off, or else a cheap pair of work gloves can lay in there.

On the smaller one it looks like possibly if you had locking wheel bolts that the "key" for removing the locking bolt (Not like a blade key, like a tool that would go into the wheel wrench) would fit in there, looks like the right dimensions.

Gilly