PATIENCE
The 4th of July is one of the busiest times. Don't expect to get right on rides, but expect a good 1 hour or longer wait for the favorites. I enjoy going to see the fireworks but I hardly go on anything on the 4th. I usually grab a margarita and go on the Mexico boat ride. There is never any wait and it is cool. And I get to drink my margarita and enjoy some quiet time.
Get to whichever park you want to be in for the fireworks and plan on staying there. I have seen MK close due to being full as early as 10 am on the 4th. In 2003 the only park that didn't close to guests was Epcot, even AK was full to capacity.
As the last poster said, bring something to cool yourself off. I hate those misters, they seem to make me hotter. The immediate mist is cool but then I feel muggy and wet, not cool. I do like the cooling neck things. There are posts where people make them themselves. I bought mine at
Walmart in the sporting area. They sell them on hangtags at the end of the aisles.
Bring in some water in plastic bottles or plan on buying alot to drink. It is important that you drink alot of water in the heat. Ask at counter service places for a glass of ice and or water. They are happy to give it to you. I usually freeze some bottles of water and carry them in a small cooler in my backpack. They thaw but stay cold most of the day. I usually stay at my DVC and have a freezer, and now most resorts have fridges free. The freezer is small but ok for 5-6 bottles.
Body glide if you are prone to blisters. Bandaids, or something to put on a sore. I don't like moleskin but alot of people do. It rolls off on me and then I have to pull it off the irritated skin and that hurts more. I prefer bandaids.
Crocs are the most comfortable shoes, but if you don't like them, make sure your shoes are well worn in. I haven't had a blister since I bought my crocs and I used to get blisters along the entire bottom of my foot by my toes every time I went to WDW.
Also, bring a few pairs, it rains alot and you won't want to wear wet shoes for a day or two, smelly, sweaty and prone to infection if you get a cut. That is another reason for Crocs, they dry out immediately and kids have the ridght idea, puddle jumping is really fun.
If your family is going to split up either bring cell phones or walkie talkies. I don't like walkie talkies because it seems everyone uses the same frequency. Or make arrangements to meet somewhere specific at a certain time. But give them a few minutes in case they were on a ride and didn't want to leave the line to get back on time. If you have ressies somewhere plan on meeting at least an hour before just in case.
I am sure I will come up with more soon, and others will be adding too this list.