I would definitely not fast like others have suggested. I'd pack some beef jerky, canned tuna/salmon, nuts, Greek yogurt, fruit, and whatever veggies I can (celery, carrots, and cauliflower seem like they'd make it). If there's a cooler I'd pack pre cooked meat and vegetables that would make it for dinner the first night and possibly lunch the second day. The rest would probably be the aforementioned items.

I would add a large chopped salad with some paleo-friendly veggies (or even a head or two of lettuce) which you can add the tuna, eggs, salami and avocados to-- or use the lettuce to make a 'sandwich' with the deli meat, the tuna, etc. For things that don't require refrigeration, consider beef jerky, roasted seaweed, nuts, nuts and more nuts.

Psilocybe Cubensis are a tasty mushroom that goes well with "primal" and music festivals.

If you eat dairy, I would definitely take some good hard cheese & nuts. Sounds like you will need the fuel for dancing!

Sardines in Olive Oil

you could always fast for 3 days. just drink water.

Use Dry Ice in your coolers. It keeps things freezer cold, and when it melts it leaves nothing since it sublimates into carbon dioxide gas. I used it a few years ago at Bonnaroo and I was surprised how well it worked.

I think all of those are good ideas, but remember to eat the perishable items first! Hard boiled eggs, for example, will last a good while but they need to be refrigerated. As long as your cooler bag stays nice and cold the eggs (and deli meat) should be fine. Certain salamis should work well, but if they are a large part of your diet you will start to feel bloated from the excess sodium intake - drink water.

Tuna or salmon in cans or pouches is a great idea for easy protein. Another idea for protein is beef jerky - you can try making it ahead of time to save cost. You can try bringing nut butter, which is a really good source of both fat and protein (and relatively low carb). Almond and coconut are my favorites.

Dried fruit is tasty and stores well but there is a ton of sugar so if you are in the 50-100 gram range on carb intake the dried fruit will probably bust your goal.

Carrots aren't a great idea; have you considered frozen spinach or other frozen leafy vegetables? If you have a stove to heat it up it could be your best option for vegetables. It's frozen so it contributes to keeping your eggs and deli meat fresh, and spinach is typically frozen in tightly pressed blocks so it will be space efficient.