I would have thought leftover beer was an oxymoron.

I think if you left it in the room with a note for the staff, then they would be okay to take it. Otherwise they may be compelled to turn it in, silly as that may sound for something like leftover food/drink. The fact that it's alcohol may make it iffier again depending upon workplace rules, etc. It's possible staff could get in trouble for possessing the stuff at work even if you rightfully left it for them, although I'm not sure how likely this problem would be.