You may bring the following items:
Blankets
Umbrellas (small hand-held style)
Soft-sided coolers
Baby Strollers
Two factory sealed water bottles up to 1 liter each
Empty Camelback or other empty plastic container (i.e., Nalgene bottle)
Binoculars
Non-professional equipment or cameras without detachable lenses
The following items are prohibited:
Weapons of any kind
Illegal substances (including narcotics) or drug paraphernalia
Framed or large backpacks
Alcohol (alcohol will be sold at the Festival)
Glass containers
Food or beverages, except for two factory sealed water bottles up to 1 liter each
Skateboards, scooters, or personal motorized vehicles
Bicycles inside Festival grounds (bike racks are available near the box office)
Carts
Large chains or spiked jewelry
Fireworks
Explosives
Large umbrellas
Chairs of any kind
Hard-sided coolers
Tents
Pets (except service dogs)
Video equipment: No video recording will be allowed
Professional still camera equipment (no detachable lenses, no tripods, big zooms, or commercial use rigs)
Any audio recording equipment
No illegal vending is permitted. No unauthorized/unlicensed vendors allowed.
No moshing, crowd surfing, and/or stage diving
Unauthorized solicitations, handbills, sampling, give-aways, etc.
Metal aerosol cans, including sunscreen in aerosol cans.
http://www.lollapalooza.com/info/faq/index.html#items