If you can volunteer for a concert or be at the premises early the next day, it is a good way to get alcohol. I have never volunteered for a local 3 day concert where alcohol is often thrown away, but that would work. I work and volunteer with a local land trust and they had a concert last night. Rich people came with wine. Less rich people came with less good wine and some beer. Most of the wine bottles and beer cans were empty while the soda cans had stuff remaining. However, there was enough fresh and good trash for breakfast this morning and half a bottle of wine a few hours later. Good luck dumpster diving.