From 11 am to 7 pm only on May 19 and 20, at participating 7-Eleven locations, bring your own qualifying cup and fill it with Slurpee for $1.50. It's the first time we've seen such container liberty from 7-11 since last March. In order to qualify, containers must fit through a 10" hole, be food-safe, and watertight. (Beer kegs and 5-gallon buckets are among those "containers" that won't work.)