Long flight alone with 5 month old?

I'm about to be taking a flight with my 5 month old, and I'll be by myself. The first flight will be about 3 1/2 hours, then on to the final destination will be about 8 1/2. I'm already a nervous flyer as it is, so I need some tips on how to keep calm while taking care of him at the same time. Any advice also on how to get some sleep? I can't take benadryl because it puts me out, and I need to be able to hear him if he cries, and I've never been able to just sleep on a plane/in a car... I plan to have him his own seat so I can use the car seat. I know to bring lots of different toys for him, and a pacifier or bottle for take off and landing. Any advice will be greatly appreciated!!