Good iced tea with fresh lime...summer is great for lemons/limes in Texas as fresh fruit arrives from the Rio Grande Valley....

Best of all if alcohol is not needed is a cold glass of ice water with fresh lime...sort of like a limeade w/o the sugar....fresh squeezed juices also are nice...

If alcohol is required, nothing beats a killer frozen margarita/mojito and Austin has some doozies for great ones...personally, I do not need the top shelf tequilas to enjoy a frozen margarita (or, on the rocks) and mojitos though I have had a few made WITH to shelf's that are plenty tasty as well, but still do not justify the extra $$$...as far as beer goes, the best I can deal with are dark Mexican beers (Negro Modelo for example)...sadly my serious beer drinking days are far behind be...

Smoothies are always a good bet....frozen fruit is available year round...they can also serve as a meal when the thermometer starts to climb....

Now, for the fast food solutions...Sonic has great malts/shakes....Whataburger also makes great shakes and a Texas institution called Dairy Queen offers great tea as well as shakes....

On the po' side (and maybe disgusting to some) is a Coke/Cherry Slurpee (mixed half & half) from 7-11!!! hahahahaha

Cheers,