If you're looking for a hydration pack, you may consider packs that are made for runners. They're usually smaller and have pockets on the straps, so you can easily access certain things without taking off the pack itself. I have extensively
researched this subject, and found two that I really liked. The first is the Wasp from Ultimate Direction, which I was lucky enough to buy used off eBay for ~$47:http://www.amazon.com/Ultimate-Directio ... 396&sr=8-1
This pack was released a couple years ago, so it's a little harder to find now. The other option I liked quite a bit is the Endurance from Nathan:http://www.amazon.com/Nathan-Endurance- ... 603&sr=1-1
Both may look really small, but if you search for them on YouTube, you can see in different reviews that they have a lot of storage space, both on the back and on the front straps. They also sit really high on the back, so they can be strapped in tight for comfort. They both have straps that have a mesh material that allows for airflow around the body, which is going to be a nice thing to have on the hot playa. I'm confident in my decision of backpack for my virgin burn!