Hi and

to both DisBoards and disABILTIES!
I would suggest you start off by looking through the disABILITIES FAQ, if you click on where it says "disABILTIES" at the top of this page it will take you to the Index. One of the top items is the "disABILTIES FAQ" which will gives lots of useful information.
Or, if you want an easier route, click on the link in my signature.
If you have to carry the medications with you, and they are temperature sensative, I would suggest that you get an insulated lunch bag of the sort that has space for gel packs on both top and bottom. You can get the packs chilled overnight in a refrigerator in your room. I would suggest taking only a minimum amount of medications with you to the parks.
If you are staying at a value resort you will have to let them know you need a refrigerator for temperature-sensitive medications, otherwise you will be charged (and I think it is currently $10 per day). Any resort Moderate or higher automatically comes with a refrigerator in the room.
Also carry some plastic zip lock sandwich size bags. If the gel packs cannot handle the temperatures for the entire day, you can ask at any counter service or beverage cart for ice, put the ice in the bags, and use that in the lunch bag.
If the heat is getting to him, you can go to First Aid in the park which will be a cool place to stay for about an hour for him to get better.
And, for a GAC you will have to let the person in Guest Raltions know what his needs are, or how his needs can be compensated for. Note that one of his needs
cannot be skipping lines.