The rest may seem a bit harsh, but honestly littering is just a combination of laziness, selfishness, bad manners and being aesthetically challenged. It's not that hard to find a bin. It's not too hard to take it with you. Don't litter public spaces - trash isn't pretty and it harms life around you especially marine life.
#1 - Part of your world? No, thanks.
#2 - Forget them not.
#3 - Love your neighbour
#4 - No mixed signals please!
#5 - Take it back.
#6 - Yay, us!
PS- This "festival" I went to was at a local beach and was very pretty, nicely decorated. It was mainly beach sports + music + dance + puppy pad - a bit hodgepodgey. While the environment was fabulous, I read a post about how these festivals could harm the beaches if proper care isn't taken. If such was the case, I should have known better so I apologise to my marine conservationist friends for not doing enough research or for not having a deeper conversations about these concerns (although I didn't really hear back from the conservationists). But if people love the beach so much, litter and marine life should be as much of a concern as enjoying it.