Deodorant.
And not just for under your arms. Any place that you might get sweaty, put the deodorant. I carry around prescription strength. I'll put it anywhere I tend to charge (happens in the summer a lot) and then reapply.
When you sweat, you also lose electrolytes, so make sure you're supplementing those as well. I drink a Poweraid a day to help; a multivitamin will also help.
Try to take AC breaks where you're in AC for at least 20 minutes. Shows are a good way to do this. You'll cool off and get an attraction in. But be warned: don't go into the AC for five minutes, then leave for five minutes, then go back in for five minutes...you'll make yourself nauseated. So for instance, when walking around World Showcase, don't shop hop quickly. Either stay in or out for 10-15 minutes as a time at least.