I totally agree with those who suggested the play areas in the parks. We went last September (aond going again this year) My son was almost 2 last year and is VERY active. He LOVED the play areas. They were great places to let him run off all his energy - he had fun playing with the other kids and with only one entrance / exit area it was a bit easier to keep track of him - but be prepared to be running around with him - DH and I took turns keeping watch.
For our flight I brought a knapsack full of quiet toys, books, etc. and his portable DVD player. Fortunately he fell asleep on take off!
I found active and noisey restaruants the best. He LOVED dinner at Whispering Chanyon in WL - especially when they yelled for the ketchup bottle because he would just yell along with them. He got ansty in Coral Reef and Le Cellier.
I brought along some of his favorite snacks and had some delivered by Gardengrocer to our resort. I made sure we had plenty of water and juce bags to keep him hydrated (ordered that from gardengrocer as well - September can be hot).
I used our own stroller - remember at the end of the day when you're leaving the parks and wiating for buses and such that's when he can be the most tired and if you
rent a stroller you will have to leave it at the park and treck to transportation and your resort without it. I know a 4yo active boy can probably run around forever, but heck, there are times I wished I could be pushed around for awhile at Disney! And if he's out of the stroller more than in it, you can always use it to store your bags and souveniers and such.
As others hav suggested - let him set the pace - take your time and enjoy.
I also suggest doing EMH if you can. I usually don't pay attendtion to EMH - it just happened one of our MK days was EMH and we had breakfast resseis in Crystal Palace so we went for EMH and got SO much done that morning. We got to do Peter Pan TWICE and IASW before breakfast then after breakfast we got in all of the big kiddie rides in Fantasyland and Tomorrowland. It was our most productive day.
Have Fun!