You have a bunch of contradicting answers. Here are my thoughts.
No car seat on the plane. The kiddo will just kick the seat in front of him (or, at least, mine did). I can't imagine installing a rear-facing carseat on the plane. That said, if your kiddo really likes to sleep in their carseat, then you could try the rear-facing one. Mine were soooo tall that would have been uncomfortable on a 15-hour flight.
If you can't get a bulk head seat, go for the last row on the airplane. It's louder (which drowns out any potential crying), easier to stand up and walk around, and will be more likely to have an empty seat or two. You are also closer to the galley and can get water, napkins, etc. if you need it.
Walk around a lot, unless he's sleeping.
Videos. Snacks. Toys. Extra clothes (for you and him).