I'd keep it to myself...He didn't buy me the car. I'd buy him coffee for straight 5 days but that's about it. Same as giving that scratch n' win package you gift someone. If they win would you expect half of it?
The buyer of the cup should say all prizes goes to him/her.Otherwise,buy your own cup.No disputes,no friendship lost.
Anyway,I found a Tim's cup that was rolled up and the prize was a free donut,whomever left it didn't care about the prize.