Water
Last year Big Day Out Melbourne hit 42 degrees. For those who don't understand what that means: it was flippin' hot. A large number of people needed to be treated for dehydration, which ended a lot of big days very early. Bring water with you - a small, pocket-sized bottle if you can manage it. There are always taps to fill up your water bottles with, so bring them along!
Painkillers
It isn't a bad idea, if it is allowed, to bring some painkillers in with you. The worst that can happen is that they be taken off you, and if the security doesn't mind then they could be a life-saver in the middle of a hot day. I stress, though that you take the advice of the company putting on the show. If they say no painkillers on the premises, then don't do it.
Sunscreen
Roll-on sunscreen is also handy to have around. The worst thing in the world is to have your glorious Soundwave Festival memories replaced with peeling skin. Again, pocket-sized is always better.
Read the crowd
Festivals are going to have drugs. It's a fact. The important thing is to make sure that you don't let them affect you. Never, I repeat, NEVER take a drink from someone you don't know, even if it's water. You don't know what it has in it and it could end your day.
Other people will be affected by drugs, so avoid them if it's at all possible.
This leads me to my next point: learn to read the crowds and, in some cases, the weather. There have already been tragedies at festivals in 2011, but that shouldn't discourage you!
Be smart. If, in a crowd, it seems like things are getting out of hand, move back. Most of the time when you do, you'll have more room to breathe and have more fun jumping and dancing with people who don't want to fight, but instead want to enjoy the multitude of bands on offer.
Organise a meet-up spot
Make sure that within your group you have a backup plan. If you plan to go to the same shows, or take the same breaks, make a designated meet-up spot. This can be a good idea if you don't want to be the creepy person at the festival on their own.
That being said, without the pressures of friends you can potentially enjoy the day more and not feel like you have to go and see Art vs Science. Because, remember, you have better taste than that.