Well it seems as though you like drinking, so I'd suggest The Campbell Apartment. Pretty cool place to go in the afternoon. http://nymag.com/listings/bar/campbell_apartment/
Best Martini I had whilst there was at a place called Langan's. http://www.langans.com/
Go to see the Upright Citizens Brigade if you get a chance. We went to the "improv night" and it was pretty funny. http://east.ucbtheatre.com/
For fine Italian dining, I'd suggest Babbo. http://www.babbonyc.com/
Sadly, you can't go to CBGB's anymore, but you could go stand on the spot to pay homage. I was very fortunate to be able to go in there just a few months before they closed it down. That's all I can think of off the top of my head. Manhattan is a really fun town! Party on!