I go to several festivals a year. They all have one thing in common. No matter how much you ask, no matter how many bins you provide, no matter what the class of festival goer. The site is left looking like a tip.
If you are old enough to go to a festival you are old enough to clear up your trash. Take black bin bags, bin your waste on the last day, leave it in or by a bin. Easy!
Camp Bestival even offer recycling facilities. There is no excuse. Don't make me tell you again.