Well, depending on who's organizing the event, there may be a variety of things you'll need. However, it's also possible that the organizers are *really* organized, and will be providing many of the things you'll be expected to use. Basic things like toilets, first aid care, and a structured schedule are usually worked into any sort of Pagan event that runs more than an afternoon. However, there's also some stuff you'll want to bring along with you: Ten Things to Take to a Pagan Festival.
If you have any doubts about whether you should take something or not, be sure to check with the folks organizing the event.
Readers, what are some things you always take with you when you hang out with the rest of the Pagan community?
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