Went to First Friday in August 2012.
There's a whole bunch of food & drink vendors. Don't be like us and get tricked into buying food from the first set of stands! We got this really bland burrito from this one truck but ended up buying more food as we kept walking around. It was probably ~100 degrees and humid that Friday so it was necessary to keep stopping for drinks and ice cream. The $5 slushie/ice cream was delicious! Also got garlic fries from this one stand; they just sprinkled a bunch of garlic powder on the fries...not actual minced garlic but the serving was pretty large for $6.
There are shops/art galleries you can check out as you're walking. There were a bunch of younger high school kids swarming around as well as families with strollers.
First Friday is something fun to do in the city, so check it out!