Thanks, Larry, for pointing out the error of consuming anything on an indoor range.
The suggestion to use a camelbak filled with ice is a good one though. I've used that for field work before phase change vests became reasonably priced.
Alternately, freeze small water filled balloons and drop them into your trouser's pockets. You'll need to bring a cooler of them, but they're much tougher than ziplocs with ice.
If you do have the money to spend, purchase a phase change cooling vest. They are effective.