I have three or four of these incredibly sturdy 17-1/2″ x 25-1/2″ x 3″ deep plastic trays from Lee Valley Tools and could certainly use three or four more. They will hold 24 four-inch pots and can be heaved around and set down with a satisfying thump. Most of the plant trays you come across are thin black plastic that break after only a season or two of use. These trays you can practically stand on, though I wouldn’t recommend such cavalier treatment of a useful thing. They can stand up to freezing cold, and long sun exposure doesn’t do much more than roughen the surface.
Mine mostly live out in the garden shed, where I use them for potting up plants and as trays for seedlings, but they’d be useful for anyone working with beads or small parts that need to be kept corralled. I think they’d be great for messy kid play as well. I’ve run into similar versions of these trays at restaurant supply houses, but the Lee Valley ones are UV stabilized plastic. At $32 each, they’re not cheap, but my ten year-old trays look a bit funky, but work just fine! If you’re going to have something made of plastic, you should at least buy stuff that’s made to last!
My only whinge about these useful trays is that they don’t nest very well. Space is at a premium in my shed, and I simply don’t have room for them. Some day, I’ll get around to building the greenhouse of my dreams, and then I’ll buy a whole fleet of them!