In case you want to capture the moment?
How do you feel when you're eating a bucket of KFC chicken? Greasy, gluttonous shame? KFC doesn't think so - they think you are having a great time, and that you might want to celebrate that party with some Polaroid selfies.
The "Memories Bucket" is going to be given away as a special limited edition to random customers. It can take and print a Polaroid picture right from the bucket, which is truly a miracle in grease-proofing.
It's also possible that KFC is going after Millennials with a canny move designed to lure in hipsters who want to eat fried chicken and take Polaroid pictures ironically. Hard to say, to be honest.