A guest post, drawing on experience, by Jenny Decimal.Bring containers for water, definitely plastic ones. Even if your tent blows up, Arcade Fire cancel due to plague related illnesses and it actually rains mud right out of the sky, you'd get by, but you won't have much fun passing out from dehydration in a moshpit.
It's tried-and-true, so it's worth repeating - aim to fill up on water well in advance and preferably at night. It's the thinnest the queues will get, and you don't want to swoon like an 18th century noblewoman when Win Butler steps off the stage, calls you by your full birth cert name and offers you his guitar on bended knee. I mean, 18th century swooning would have been cool for Funeral, but we're kicking Suburbs stylee now. The point is, don't leave it until the very last minute or when your very favourite band is on to try and get water. That's invariably when squintymillion other people are in the queue in front of you and then the taps fail. This philosophy can also be applied to toilets - go when you can, so you won't need to when you can't.
Of course, if you're trying to spend a load of time in the pit, balance your need to actually live with your need to stay in the pit without having to pee, but either way it's better to have the water to hand if you need it. Also bring lots of bottle caps in your pockets. As you're entering the arena, take the lid off any bottles you have and stow 'em, or they'll take them from you. It's stupid, but do it. You are allowed bring cans and plastic bottles into the campsite, but no glass, and nothing into the arena itself. Pints of watery Heineken are ten bucks in there though, so be creative. There are variations on the idea of the "decoy can", but I'll leave the rest to you.
Wear clothes you're prepared to dump. Keep a couple of essentials - underwear, socks, facecloth, TOILETPAPERTOILETPAPERTOILETPAPER etc - wrapped in a little plastic bag, but whatever you bring you may have to carry - Make sure it's stuff you can't live without it. Get cheap ass toilet paper and lots of it - the less fluffy it is, the less space it takes up and the less mushy it'll get if it does get a bit damp. If you can pull the cardboard roll out of the middle to squish it further, all the better. The sensation of pulling on fresh, dry socks on a pissy day is better than sex with God. Savour it, protect it, mind those socks like you'd mind a child you're particularly fond of.
Bring snacks. Mars bars will fill you up and give you energy but are manky. It is possible to live off them for about three days without any ill effects, and I've done it, but I never, ever, ever want to see one again in my life. Muesli bars will fill you up and have a bit of texture, but are the world's single most depressing foodstuff. Salty things will satisfy a craving, but will make you thirsty and tend to take up more space than they deserve. Tinned fruit salad is heavy, but will make you cry with joy by day 3 - just make sure and get a ring pull one, genius and bring something to eat it with. Treat yourself to one hot meal a day, and choose it carefully.
Boozewise, remember that everything has to be in plastic containers. Bring something you enjoy drinking, not something that will get you drunk in half a second just for the sake of it. Beer is incredibly expensive in the arena, so do bring something, but bear in mind that a load of cans will make you want to pee all the time. Bring a spirit maybe, but don't be a knob and drink it all neat. I recommend Lidl's I Can't Believe It's Not Martini own brand Vermouth, it's cheap, summery, very drinkable and mixes well with lots of things. Likewise, but a little less so, for their gin. Avoid their rum at all costs, it is poison. The vodka sounds badass at the time, but just... don't. A festival hangover is not in the least bit fun, and has cost many people a fine Saturday's lineup. Regarding drugs - make your own choices, but make good ones. Don't show off, don't be an idiot, and don't spend two hundred and fifty euro to spend a weekend wrapped in your sleeping bag screaming at your own feet. Contrary to popular legend, a loud and occasionally rowdy music festival is not necessarily the best setting to embark on a new leg of your chemical adventure, so think carefully. The best advice I ever heard in this area was to write the words "You are on drugs, enjoy yourself" on the back of one of your hands, but this might present it's own problems when it comes to displaying your wristband to security. Drink or drugs, remember - You're aiming to get pleasantly and amiably buzzed, not on the news.
If you're bringing shiny new novelty flowery wellies, make sure they fit you like a handtailored condom. Too big or too small, they will mash your feet into weepy stumps. If possible, and if none of your neighbours can see into your house, wear them around over the next week to break 'em in. It might be worth bringing very light runners this year. Might. Cheap, light, disposable Primark runners, to give your feet a break from wellies. But only if it's dry enough.
Waterproofs might be a good idea, but anything plasticky next to your skin will sweat you and could chafe in all sorts of nasty places. Is it worth it to stay dry? Probably, but if the sun comes out you'll cook. If you can get one of those teeny little jacket type things that scrunch up to about the size of a fist, that could be cool. I don't know, to be honest, I can't decide. Umbrellas are a no-no for the audience. They're awkward to carry through a crowd, they obstruct the view, and they're too damn pokey. Might be worth stowing one in your tent for trips to the taps or toilets though.
Glowsticks make me profoundly happy generally, but they're also a handy lightsource that doesn't need batteries and doesn't care about getting wet. You can get the chunky ones in a toy shop for cheaper than you would in a camping shop, or the little glow bracelets are dirt cheap in a €2 Shop on Liffey Street. Do bring a little torch though, preferably a likkle maglite or similar. Glowsticks are a surprisingly effective back up, but they're no substitute for a proper beam. Strappy headlamp if possible - there are many entertaining and necessary things at a festival which will go more smoothly with both hands free. Your own light source becomes very important when the last act ends, and don't you forget it.
Baby wipes are a very, very good idea, but get ones that aren't too sickly sweet and won't leave you sticky. I prefer Simple, and Pennys very often have these in a two-for-one deal. Come to terms with the fact that you'll probably smell anyway. It's one of the only occasions in the year when that's cool, so embrace it. Reek with pride -but do bring some manner of deodorant, I mean, you're not a savage. A water bottle with a bit of shower gel and a sports cap on it can work as a manky knacker shower in a pinch, but be aware that if anybody sees you doing it you'll never quite have the same relationship again.
Your phone might or might not work with that much network activity, but all the same, it's well worth having a look in Maplins for one of those solar phone chargers or one of the ones that uses AAA batteries. Arrange a landmark to meet your mates at when/ if you get separated. Sounds lame, sounds mammyish, it works and it has saved me a lot of unpleasantness in the past. The first big, visible thing that you see, that's your meeting point should things go arseways, and make sure everybody knows it. It is not funny trying to find your mates in an emergency when there are thousands of other mud covered gobshites wandering around just as aimlessly and nobody has a working phone. Don't bother with walkie talkies - some MENSA candidate always has this idea, and drags the bastard things there, only to realise all he can hear is 32 types of parking attendant traffic and one other stranger who's also had the same idea and can't get hold of his friend either.
Lastly, the obvious stuff. If you're camping, walk through fire to camp next to people you know. Don't camp on the edge of the site, or somebody will piss on or fall into your tent before the night it through. Don't leave anything valuabe in your tent. Get a decent tent with an outer and an inner skin. Those 10 quid ones that are only one skin are crap, but you can get decent ones in Argos for a decent price. Make sure it's the right size - if anything is touching the inner skin to the outer skin, you'll get a wet tent. Set it up as soon as you get the chance, early in the day before it's dark and before the only place left is the bit of the field everyone else calls "the shitehole", right next to the molotov-juggling heroin-dealing gunsmugglers. It's worth figuring out your tent before then, so maybe try setting it up once or twice this week.
Don't camp close enough to the toilets to smell them, don't camp far away enough that you can't make it there in a hurry. Don't camp on the outer edge of the site, or on the edge of any path to anything, ever.
I think that's pretty much all I can think of...
Oh, don't let Win Butler mind your basketball, you'll never see the bastard again.