Gigs can be very sweaty and smelly experiences. If you're prone to bad body odor then maybe a squirt of anti-persperant or a shower before the gig would be a good idea. I've never understood why before a band even starts people go to the gig stinking of B.O.
Don't try to sneak out a nasty fart just because you're in a large group of people thinking you'll get away with it. People will figure out where the smell is originating from and you don't want to be 'that guy'.