Sitting around generating random energy thingys for no good reason makes people look at you funny, and it can wear you out if you're still learning how to ground. Usually public events have a site fee. Remember, Pagans don't have paid clergy, and if those attending the ritual don't pitch in for space rental, cakes and ale, and fliers, it comes out of the ritualists' pockets. On the other hand, if you really can't afford to pay, it is reasonable to ask to help clean up or something in exchange for attending. Buying lots of disposables for a ritual not only causes the host group to jack up the site fee to cover expenses, it creates lots of waste that will sit in a landfill for a very, very long time.
Energy work can be very draining, and it's important to have plenty of substantial food available.
If you are drunk, stoned, or on strong prescription drugs, you do not belong in circle. These things can disrupt your energy pattern and interfere with circle work. The exception to this is if you need to take prescription medicine to regulate your mood or personality. If you want to see how a particular group works, contact them to find out the procedure for visiting one of their events. Some groups require sponsorship for guests.