Camping is the way to go.
If the festival allows for camping, do it. The ticket may cost a little extra to include the camping but in almost all cases it is still cheaper than getting a hotel room for a few nights. Camping is also a huge part of the music festival experience that you do not want to miss.
Bring whatever money you’ll need with you.
Bring cash with you and limit yourself. If you bring too much you will be too willing to spend it all. Also, ATM’s charge fees for transactions. It may only be $5 but every penny counts right?