Over the years, I've collected a motley batch of shallow trays to put parts in (temporarily) while working on my Fly Baby. Most of these are from Vishnu knows where...just some plastic tray about the size of a paperback book that'll sit on the wing and keep all the cowling screws in one place without scratching the paint.
Discovered a great product for this... the Ziploc folks, who make the sealable bags, also produce a series of disposable food containers. These are perfect... plastic, various sizes, even a lid if you want to avoid the scattering effect if a power cord or air line brushes them.
Best of all, they're cheap: About a buck each, in sets of five.
They're available in the food section at Target, Walmart, etc.