I have been traveling with my children since they were just a few weeks old. They are now almost-4 and almost-2. When it comes to plane rides, the best thing to do for ear pressure is to nurse or give a bottle during take off and landing. Otherwise, give him a little snack so he's working his jaw. To entertain, think about the things he likes to do when he's sitting now. Small board books like My First ABCs are great- full of color and different pictures you can point out to him. Activity books or stuffed animals that have things like zippers and buttons and shoe strings are good. He likely won't be able to actually do the things, but he'd love to play with the buttons, zippers, etc. and try. Take some things he already has, but maybe get a couple of things new so it's a big treat for him. Hand puppets are always fun, easy to pack and you can make up a lot of games with them- hide and seek, peek-a-boo, tickle him, sing songs, pat-a-cake. The best thing is if you can get him to sleep.
You should also take plenty of food and snacks. Snacks always keep my kids entertained- cheerios, cut-up fruit, whatever he likes. For meals, if you can, try to feed him before you get on the plane because it's pretty cramped on the plane. If you get a plane that has a changing table in the bathroom, it will be very small. If your plane doesn't have a changing table, you will probably have to put him on the floor in the kitchen area to change him. Definitely take something to lay him on for diaper changes. I also take a few plastic bags- 1/2 or 1 gallon size- they hold dirty diapers (you have to put them in something on a plane or the whole plane smells), or dirty bibs or clothes, and one for garbage. The attendants never come around enough to collect all the garbage you may have with a little one- napkins, wipes, snack bits, etc. Hand sanitizer for the both of you is a must. And so is at least one extra outfit for him and you. I also always take a lightweight blanket- it can be a pillow for him, a cushion for your arm if he falls asleep or cover him if he's cold.
Definitely take a stroller for the airports. They are a pain to go through security with, but make getting through the airports so much easier.
If he cries or fusses a lot, you will get dirty looks from those around you. Ignore them- you'll never have to see them again. Good luck and enjoy your trip.