Whats a good standard tip?

I'm visiting New Orleans this weekend, and I want to make sure I'm a good tourist. The FAQ made it seem like tipping is an important aspect to that, so I wanted to make sure I'm prepared and not some cheap jerk.

I tip 20% on all restaurant/bar tabs, that's standard, but I don't have a lot of experience with tours guides or street/bar musicians and the like, especially since I typically don't have carry cash anymore. My intention was to get a stack of $5 bills in my wallet and just hand those out as needed depending on the service.

Any advice would be appreciative, and since your here, a bar recommendation near St Charles and Jackson, my wife and I are staying at the St Charles Coach house. She likes cocktails and wine, I drink beer but am flexible.

Thanks!