If you do get bumped, as said in the other posts, your luggage will go without you. Make sure to ask the airline if they give any vouchers for incidentals. On an AirTran flight 4 families gave up their seats since the flight was full. The woman ahead of me, who had obviously done this before, asked about it and the airline gave us $25.00 per person to buy clothes, toothbrush, whatever you wanted. This was $100.00 for my family!! On top of vouchers for bfast, lunch and dinner and a free night at the airport hotel and free roundtrip tickets. I don't think the airline would have offered if the woman had not asked about it. Airlines probably vary on this policy, AirTran is awesome in my opinion, so they may be the only ones doing it, but it doesnt hurt to ask.