This was about 20 minutes before the cosplay show at Mizuumi-Con on Saturday, March 31st, 2012.
I had passed by a vendor selling these Mario Mushroom candy tins, and I didn't think much about it until the show organizers said that the schedule had been pushed back by 45 minutes; that's when it popped into my head that I could get a 1-Up Mushroom Tin to use in the show.

BTW, the act I did in the show was a small pantomime of a general SMB game scene: Throwing fireballs at an enemy, and then punching a block to find a hidden 1-Up Mushroom! 8D
It think it's a day celebrated only in the UK.