I would put ice cubes in the jars and if you don't have a cooler, put them in travel mugs with ice cubes. It will water them down a smidge, but at least it will keep them fresh. I wouldn't let mine sit in a glass for a few hours in that hot of a temp. and I like mine over ice so it is a chilled drink.
You figure they keep the coconuts in a refrigerated section at the grocery stores for a reason, you definitely do not want to take a chance and end up drinking coconut water that is going bad! Bacteria can grow rapidly in warm temps.