Hi L. - my little guy (now 7 mos.) has been from Los Angeles to PA to TX and around again since he was 5 months old. We did Southwest a lot, which I recommend when you can because of their "chose your seat" policy. They also offer infant fares (though sometimes the internet specials are actually cheaper).
You might want to call and see if there are any seats available and if the airline has an infant fare. Maybe you can get a seat for him. If not, definitely request a bulkhead, and ask if the airline has a "bulkhead bassinet" - not all airlines do, but obviously, the bulkhead will give you some extra floor space for baby to lie on. Ask for extra blankets though, because the plane floor is cold. Also, I use an ERGO baby carrier and I LOVE it - front carry is very handy - they can hear your heart, and can even nurse in the carrier. Once the baby is old enough to be carried "piggy back", traveling is even easier. Check out ergobabycarrier.com - click support, then instructions and you can see the video on how it works. They've also updated some features, so it's even better now.
Also, bring an EMPTY water bottle with you into the airport, and use the fountains to get more water if you want to save $ and not buy overpriced water in the terminal. If you're breastfeeding, you need all the water you can get, and you can also breastfeed during takeoff/landing since he doesn't have a seat.
Check the weather (weather.com) re. clothes - my little guy was in warm climates and lived in onesies for the first few months of his life. Sunscreen isn't really recommended under 6 monthes, but check w/your pediatrician. If they say no, you'll want lightweight clothes that cover the baby's arms and legs, and also a hat. Have fun!