I love this question, David, for the entirely narcissistic reason that it captures so much about my own teenage years. On the one hand, your daughter is probably fit to burst about her incipient weekend of wild adult independence. On the other, she is panicking about her wardrobe to such an extent that her father is stepping up to the bat, ready to brave the terror that is River Island in the middle of festival season, just to make his darling little girl happy.

For my 12th birthday, my parents got me a ticket to Madonna’s Blond Ambition tour, thus acknowledging my imminent crossover from child to teenager. I knew that once I went to this concert I would be a changed person. But because I couldn’t possibly go to Wembley on my own, and my parents would rather eat their hair than go to a Madonna concert, they bought another ticket for Michelle, the New Zealand student who lived with us, in exchange for childcare. So, in other words, I went to see Madonna with my nanny. Hello, maturity!

“What is she doing?” I remember asking at one point when Madonna frantically rubbed a crucifix against her crotch.

“Er, I think she has an itch?” Michelle replied.

“Ah right,” I said, which made sense, as what else could she possibly be doing? Truly, as Kevin from The Wonder Years would say, I really grew up that night and nothing was ever the same again.

But to your question, David. Regular readers might be feeling a sense of deja vu here, because, yes, I have been known to write about Glastonbury fashion before. In fact, I would estimate that I have written about it every summer I have been at the Guardian, meaning I have now written about it a, frankly, midlife crisis-inducing 16 times before, and that is because I am on a righteous crusade here. This, dammit, is my cause, one that I feel sure will one day net me not just the Pulitzer but the Orwell and quite possibly the Nobel: I will not rest until I finally put paid to the ridiculous idea promoted by, er, the media that Glastonbury is in any way about being fashionable. Maybe it is for celebrities who fly in and out by helicopter from Babington House, but, for everyone else, it is and should be about one thing only: survival.

It would be tasteless, wrong and quite possibly a sackable offence to describe Glastonbury as my annual Vietnam – to paraphrase the Dude, what the fuck does Glastonbury have to do with Vietnam? But it should be approached like an endurance test, which, in my case, means dry shampoo and wet wipes. The idea that anyone – literally, anyone – on that site cares what Grazia thinks about their outfit while they’re trying to navigate the portable toilets without catching an infection is a myth that can only be maintained by someone who has not been to the festival.

Earlier this year I went to Coachella in Palm Springs, California, for work (I know, I am literally a coal miner) and that is quite a revelation for someone who has only ever been to British festivals, because the differences between the two festivals exemplify the differences between Britain and the US. While British people gripe that Glastonbury is all gentrified and middle-class now, Coachella laughs and says, “Hold my cold-pressed green juice.” Aside from being actually sunny and beautiful – it’s held on a polo ground – Coachella has things like a pop-up Sephora (basically, the American equivalent of Space NK), air-conditioned dance tents and places to sit. In other words, it is a pleasure to be at and proud of it, because it is American, and in the US, convenience and personal comfort are part of the constitution. Glastonbury, by contrast, takes the entirely British point of view that convenience is shameful and being uncomfortable is an essential part of the experience, which is why so many people in this country spend so much money every year to stand in an overcrowded field in Somerset for three days with only dreams of indoor plumbing to get them through the wet, cold nights.

Anyway, my point, eventually, David, is that your lovely daughter doesn’t need anything special for Glastonbury: a waterproof and a warm jacket, a zip-up bag (so nothing falls out), wellingtons, long socks, sweatshirts and minimal toiletries. Maybe makeup, if she can be bothered, which I definitely cannot, because, really, who can be bothered to take off their makeup at 4am when they finally return to their tent?

There is no way your daughter will believe you when you tell her this but the real sign of adulthood is not fitting in but learning not to give a toss about what anyone else thinks. This means not worrying if you are “on trend” at Glastonbury, or if you understand everything Madonna does, or what others think of you, full stop. The best experience she could possibly have at the festival is just to have fun: dance like a fool in the dance tent at three in the afternoon, fall over and walk around covered in mud for two days. But it takes some of us well into our 30s before we reach that level of maturity.