Wow...you have gotten some excellent advice. The only other thing I would offer is to let your airline know ahead of time. There are notes sections on your reservations on their computer. Call them now and let them know you will be checking medical supplies and then tell them again when you confirm your flight the day before, and obviously when you are checking in. Reiterate to them how important the supplies are to your special needs son. If anything were to be misplaced you could let the airline know that you gave them advanced notice, notice the day before and notice when you checked in and that the formula is medically necessary and they need to expedite finding it or replacing and delivering it by the end of the business day. If you have alerted them (multiple times) and something were to happen, I am sure they would bend over backwards to get it resolved right away.
~Elisa
Thanks, I'll remember to do that once I book our flight. Here's to hoping Southwest has decent rates on their release on Friday.