I also do this with beer or leave partially finished bottles of Scotch (decent single malt). I hate leaving the latter but this is often much better for me than trying to kill the bottle the night before!
A couple weeks ago, in Myanmar, the maid came running from my villa to give me a 1/4 bottle of Aberlour. I just gave it to the European staff there who were quite pleased.
I do not consider this an acceptable replacement for a cash tip in places where tipping is expected though.