Drink lots of water. I mention it every year. Actually do it. You can get dehydrated super fast.
Shows don’t always start/end on time. This is especially true for the Club Crawl. Outdoor stages tend to work like clockwork but don’t be surprised if you head to a club and see your favorite band is half-way through a set.
Don’t set your stuff down and assume it will be there later. Seriously, there is no magical theft-proof corner of the 40 Watt, despite what has been claimed. Travel light and keep tight.
Take multiple breaks. Sitting down for a bit is wonderful. Hop into a beer tent or find a venue with A/C and chairs. You’ll be standing and walking a lot so this will help you keep going.
Take and tag pictures. If you’re the Facebook kind, tag the pictures you take of bands. It helps them reach more fans and helps you connect to other music lovers.
Sunglasses, hat, sunscreen. YOU WILL BURN.
Umbrella, in case it rains. Also, make sure to keep up on Athens GA Weather’s blog.
CASH. Many of the artists’ booths and band merch areas aren’t card capable. Bring some cash with you to buy those shirts and stuff, ok?
Identification. HOW TO GET INTO A VENUE: Step 1) Have id card in hand when approaching the door Step 2) Have money/wristband/pass ready when approaching door Step 3) Hand over id, get hand stamped or wristband attached
Comfy shoes. Lots of walking doesn’t need to lead to lots of blisters or aching feet. Flip flops sound like a cool idea until your arches are killing you.
There are venue schedules posted at almost every door and Flagpole guides are everywhere. If you’re still unsure when your band goes on, check out the Athfest app. Or here. Or Echoreyn of Athens. 🙂
Overall, just be safe, sensible, and have a lot of fun!
athensmusicjunkie.com 
Good for you for mentioning hat, sunglasses and proper sun protection.
I get looked at like I'm from Mars because I cover dress in what amounts to desert survival clothing.
At the end of the day, I'm a Georgian to the core, and I've adapted enough to the ungodly conditions to be able to wear the stuff.
If you are not, I can not stress enough wearing it anyway and, as you say, drinking lots of water.
I may look funny, but at the end of the day I don't smell any worse than the rest of the great unwashed throng, and I don't look like a gigantic wrinkle bag beet.
People are so short sighted sometimes.
Anyways, it's going to be a scorcher this year for sure, music and weather wise.
Great job as always.