We traveled Thanksgiving weekend and could have avoided the baggage fees from United.  The airplane was fully booked so they requested travelers to check their carry-ons at the gate because there would not be enough room in the overhead bins.  If you check your bag at the gate it is free.  We checked 1 large suitcase at the check-in counter for a cost of $25 each way and we could have avoided this charge by taking 2 smaller suitcases and then check them at the gate if they did not fit.  It pays to be an experience traveler, so the next time we travel domestically we will be sure to max out the carry-on policy of 1 personal item and 1 carry-on suitcase.  Lesson learned and is a valuable travel tip.