I'll second Kozmo's set Tales from the Street. A great product for the beginner busker.
If you're busking, you want to put a few 'hat lines' throughout your performance, not just at the end. I generally go with 3 of them. One near the beginning which is half a joke, something like, "Annnd that's why I have to work for tips" (Usually when it seems like I've messed up). One around 2/3 the way through, a bit more direct, "Something I want you guys to know, all those other performers here are getting paid by the city (or whatever) . I'm not. I get paid by you. I know, I don't like it any more than you do." And then at the end of the show I outright ask for tips, "If you enjoyed the show please drop a little something into my tip basket there, this lets me keep coming back and performing for people like yourselves."
Those lines are borrowed and not an exact script, just the general idea of what I'd say.
I don't think it's a big deal to perform some of the same tricks in both places. However, I would not do your 'big trick' for the streets. Save that for the paying audience so that you have that ace up your sleeve.