Final presentation coming up real soon and I could use some help with colloquial spanish.

Situation 1: You're talking to your grandson and tell him that you've got a present for him if he's been good. His reply is "I've been good."

What would be the most gramatically correct translation and what would the child actually say?

(Probably the most difficult topic for me so far has been the varying past tenses. Can't get it through my skull which one to use when).

Situation 2: At the end of your three minute set at open-mic night at your local spanish class (errrrrr.........comedy club), how would you say

"Don't forget to tip your servers"

Thanks once again to everybody for your help.

........Rich