some ideas: -
Breakfast - We usually cooked at the tent ( spahetti, beans, tomatoes, sausages all kept in a cool box with ice ok for a couple of days along with some yogurts), took apples as they last the journey or heat, def take some aplen bars.
Lunch and Dinner - In the arena there are loads of places to eat - Loads of baked potato, veggie stalls with falafels and salad, or I found a farm stall where I got some steak and onoins without the bread
night time snacks Whilst everyone was munching on pringles, haribo etc I took some mugshots and quavers ( 3or 4 syns)
When I am at a festival I was absolutely drinking which TBH was hard to syn as there was a lot of it

but by eating right I knew I had some kind of damage limitation and saved a bit of money as I cooked my breakfast and dinner.
Whatever you do have loads of fun and if you do over indulge - at least you had a ball and can get back on track once your hangover goes away
Lisa xx