First plan ride with 8mo. tips and advice pls

So I'll be traveling at the end of the month with my son. This will be his first time on a plane so I have no idea how he's going to Handel it. the flight will be about 5hours. I want to travel as light as possible! I won't be getting an extra seat for him because I don't have the budget for it. I plan on holding him is a body carrier and just having his diaper bag. Any tips or advice would be great, please and thank you. 
Tips on: 
-Carrying baby food on plan
-smoothie him
-checking in car seat/stroller. 
P.s I never took notice but do they have a changing table in the bathrooms on the plan?