So I found a great little thing the last time I went in the summer. You know those stick on gel packs they sell to help fevers in children? You buy those and instead of sticking it to your head you stick it either to the back of your neck right under your hairline of between your shoulder blades. I also thought maybe the small of your back would be a good spot as well. The exact brand I used were the BeKoool. The come in a 4 pack for about 3 to 4 dollars. You can pick them up at Wal-Mart, Target, and almost every drug store.
I used them in our last July trip and never once broke a sweat. At one point everyone else was complaining about the heat and I was like what it isn't that hot. I had forgotten I had the patch on because they work for up to 8 hours. Once I took it off because the sticky was wearing out I got hot and sweaty and decided to put on the back up one I packed for later that day. When you first put it on you can tell how chilly it is.