1. Get there early to avoid lines.
2. Bring a blanket. It can some time be a bit of a pain in the ass to carry around, but if you bring a bag you'll be fine. At a festival of the scale of ultra the blanket will serve many a purpose. Just lay it down and it instantly becomes the meeting point and resting spot. At some point you will probably get lost, its nice to have a a spot to go back to. The blanket is also a social tool. It's great for making new friends that just want a place to sit other than the dirty floor. Sometimes those new found friend will carry party favors, will share in appreciation.
3. Toilet paper. That's right TP or baby wipes are a hot commodity at large festivals, especially toward the end. TP is an excellent trading tool, when you get in line to go to the port-a-potty it's an express pass to the front. Just break of some squares to the first person in line. You'll be like an angel dropping from above, they'll be more then happy to let you cut in. I've done this in the past at Ultra. One guy even offered me $5 for toilet paper, I felt bad so i just gave him some squares.