Vector Force's Two Payloads

I'm using half of the top payload bay for an altimeter, but the other half is free.  As for the bottom, larger payload tube, I can't think of anything that needs boosting in there. It is available for hire, but only to about 400 feet on a C motor.  I'm going to try this heavy bird with a composite D10 motor and see if I can hit 1000 feet. So I guess I'll put a beeper in the lower payload to help me find this after the flight.