SK1 is craigslist slang for SKI (i guess they think they're fooling big brother by throwing a numeral in there) which is done on snow which is another word for cocaine because they are both white and powdery
Learn something new everyday. I knew the party part of the advertisement probably ment recreational drugs, but had no idea what sk1 was, or pnp for that matter. 420 is about all I know. Thanks for the info. Think I'll stay clear of that one.