Well. To accurately adress this situation, we'd have to weigh the pro's and con's.
Let's say you were the sort of chap to enjoy the smoking of this substance. There are the possibilities that you'd be caught by the police or something while removing the said bag from it's current position. Or even worse. There was a drug deal going down, and you made an attempt to run away with their goods. That won't end well. Or of course, someone might have tampered with the stuff, leaving you unknowing of what you're actually smoking. Now - does the enjoyment you could derive from this weigh up for all of these possible scenarios? If so, then I'm sure I'd take it. If not so much, I'd probably take it anyway. If very little so, I'd leave it for someone else to find.
Now if you weren't into this kind of stuff you'd have two possibillities. Take it and sell it onward, or bringing it to the police. Say you bring it to the police - what is your reward? Next to nothing, perhaps a pat on the shoulder if you're lucky enough to not be considered a suspect of possessing or dealing. If you do decide to sell it, you'll have to get down to the parts of the society where this is possible. These parts are usually not know for their hospitality. Therefor, if you're not really used to dealing with this stuff, you might just end up mugged, beaten and perhaps stripped of some clothing. No reward for you what so ever. Still possibly better than being looked upon with suspicion by the cops. Now if you were to be able to handle the drugdealing thing. Then you might just wind up with a load of hard cash. And that certainly would be pleasent.
With that summary, I'd say the two most valid option would be to smoke it yourself or sell it onward. You decide, kids. And remember:
Just say No
