I haven't read all of the responses so I'm sorry if any of this has already been said. Here's my two cents for what it's worth:
1. First of all, don't worry about other people. You have to worry about your family. You will likely never see the same people twice anyway.
2. Talk to him ahead of time about your basic plans (not discipline, just plans). i.e., if you are going to go back to your hotel for a midday break, let him know that is part of the plan ahead of time so he is prepared for/expecting it. Don't just thrust it on him.
3. Do take a break! Not just meals. WDW is a lot of walking and the FL sun can wear out even the most physically fit. Plan some down time in the middle of the day so all of you can rest and refresh. Going back to the hotel can be good...lounge at the pool for a bit maybe.
4. Take the park slowly. It's not a marathon. You will NEVER do everything you want. Enjoy the time rather than rushing everywhere.
5. Let him help plan your days! He might enjoy being in control of a few details (such as rides/restaurants).
6. If you start to see signs that a meltdown might happen, try to steer him in a different direction before it spirals out of control. I don't know how this works for you. My kids are completely different so what works for one does NOT work for the next one. YOu have to know your child here.
7. Ah...discipline. This is the fun one. How to handle it. I'm assuming you're traveling with his father as well so forgive me if I'm mistaken. I would discuss with "dad" your concerns and create a plan of action. This could even include some options for the various behavior issues with appropriate discipline for certain infractions. i.e.: if he says "no" to you guys it might mean missing out on dessert whereas full out tantrums might mean sitting in a quiet spot for a preset amount of time. Once again, you need to know what works best with your child. If you are worried about a fit over souvenirs, create a spending limit and maybe even give him the power to do the spending! This is a good way to teach him how money works anyway.
I can't think of anything else right now, but hopefully this is of some help. Have fun! Try to remain cheerful no matter what. And make sure you do what is best/right for your family without worrying about the other people who might stare. People are judgmental all the time anyway. You have to teach/mold your child....their stares won't change his behavior. Only you can.
