The countertops that flank most cheap BBQs are fairly breakable, and can get gross pretty easily as dust settles into their crevices. If they aren't cutting it anymore, you can class your BBQ up with some cheap TV trays.
Once you find some suitable TV trays, you'll want to remove their legs, and apply a solid coat of water seal to the trays themselves. Once they're dry, take the side tables off of your grill, along with any excess plastic bits that held them in place, making sure to salvage the screws and bolts. Then, mark where the new tray will attach, and bore out some holes with a spade bit and a drill. Attach the bolts with some wood glue, and you've got yourself faux butcher side tables that will make seriously beef up your BBQ.
Even with water seal, this trick is probably safer if you keep your BBQ covered most of the time, but the trays should hold up well with minimal care. Be sure to check out the Instructable for a complete guide.
DIY Grill Side Tables [Instructables