At work, I use my cheap plastic office inbox tray to transport stuff. It's very light with 3 raise sides and is made to be stackable with identical units. The cost was about $5 (government discount included).

At home, I have a lightweight resin bread cutting board that works fine. If required, I lay a dry cloth as a friction surface on top and use an oven mitt underneath if I need it to be perfectly level on my lap.