Assuming your not allowed to modify the gearboxes or use different motors than the other teams. You could use the smallest drive wheel you can to increase torque. Double up on the wheels for more traction (like a dually pickup truck).

Another option is to drive a secondary reduction off your gearbox. I.e. put a small gear or sprocket on the gearbox output shaft which would be driving a larger gear or sprocket attached to your drive wheel.

Steve