I have an inexpensive tool cart, which has my air tools in a drawer. I modified it to fit my small air compressor underneath and a hose reel on the side. In the tray on top, I was collecting a lot of miscellaneous junk. I have wanted a hard flat surface to align and measure things. I had some leftover granite countertop, so I cut it to fit in the tray. I built it up underneath with wood and leveled it (more or less) with shims so the granite top is slightly above the rim of the tray.
Let's see how it goes, and I'll post an update. So far I like that it's easy to clean off when I'm done working on something messy and it's not so tempting to collect junk on it.