Many times events such as carnivals and fund-raising events sell tickets for an opportunity to stick your hand in a bag and pull out a prize. Imagine what emotions your character will experience contemplating putting their hand inside a closed-off bag or box.
He might be a bit scared, wondering if he’ll touch something slimy or gooey. Or he might be in for the fun, no worries, no concerns.
Perhaps he’s got a few friends watching. Imagine what they’d say, how he’d react. Is he the kind who accepts friendly ribbing or would he get angry?
When his fingers touch whatever is there, what reactions does he have? Does he make a face or laugh? Retract his hand without taking anything?
Your task is to write the story of the grab bag.
Establish scene and circumstances through a few descriptions of setting. Identify major characters though one of two details at most. Let there be dialogue.
Have fun with this one.