First - things you really do need, unless you are extremely hardcore.
- Tickets - the average festival, even a free one will need to count people that are attending. So be sure to get a ticket. Some festivals sell 'at the gate' but not all and you could be disappointed. Some planning for this is wise.
- Your festival home - Tent, bed and sleeping bag, also some clothes. I like to have a dry spot in case of rain so I go with a tent, if you are camping in an extremely sunny location you may feel an all weather sleeping bag will do - or you may think you will rave all night and sleep in the day. Good luck with that. Take wellies.
- Money - You will probably want to buy food and some beer. I know I will. Take money. Many festivals now have cash point machines. Take your cards too but keep them safe. Don't leave valuables in your tent. Sleep with valuables in your sleeping bag.
- Hygiene essentials - Toilet paper, wet wipes, anti bacterial hand gel. Festivals start off 'toilet paper rich' but this can dwindle. Water will be available but wet wipes and hand gel will save queueing and allow you to 'wash' in the tent.
- A torch - if you plan to find your tent after dark even the best lit festival site can do with extra light, and a toilet can be a scarier place in the dark where you can't see what is 'wet' and what isn't. A head torch is good in this situation.
and now stuff you don't need
- lots of things sold with the word 'festival' as a suffix. Like festival emergency poncho - use a bin bag or, radically, a coat. if it's warm don't even bother, just have a dry change of clothes in the tent. Festival shoe covers which are just fancy plastic bags for people that can't be bothered to buy wellies. Buy wellies.
- Festival Trolley - trolleys are great, I have one, but you can hire or borrow one at the site, not an essential.
- Phone charger - yes it can be useful to use your phone but lots of sites have poor reception, and often they have charging points anyway. If you do bring your phone, why not save a few minutes each evening to tweet/send emails/check texts and just save the battery.
- Dry Shampoo, or solar showers. There are showers at most festivals...with queues a mile long. You may be tempted to use them. If your festival is less than a week long just embrace the grunge. Use a wet wipe, stick your head under a tap. Dry shampoo will make you prematurely gray and flaky, a solar shower will just annoy nearby campers.
- Drugs - no one needs to get arrested, and if the festival is a good one you'll be having lots of fun without drugs. Don't dull your experience, tune in to the festival vibe, get high on that...and drink some more beer.