In general, the average tip is around $5.00 per Queen per a performance.
If you're feeling generous, tipping is always an option! It's completely up to you whether you want to leave a tip or not. If you had a fabulous time and want to show your appreciation, a tip of $5.00 is generally considered appropriate. But if the performance blew you away, don't be afraid to be more generous. 
On the other hand, if the performance didn't quite hit the mark for you, feel free to tip less or not at all. And if you're a little nervous about interacting with the fabulous Queen at your first drag brunch, just break eye contact after leaving a tip. No pressure, just enjoy the show!