The ergonomics of using a laptop on an economy-class tray table are not worth it. You're sitting there like a T-rex

The trick I've found is to pack a bluetooth keyboard. If you put your laptop on the tray table, you can put the bluetooth keyboard on your legs _under_ the tray table and have your arms fully and comfortably extended. This works especially well if you're a vim/emacs/other keyboard driven editor user as you very rarely need to reach up to poke the trackpad .