Originally Posted by Bikingscott

Make the non-rev reservation (PNR) then you can check-in and check bags to your final destination. This is especially helpful if you are making connections.
If the flight is full, tell the gate agent that you are listed as standby, with a bag, and you want to Jumpseat (OMC, on UA)
They simply convert your PNR to OMC, and you and your bag are on.
BS.