Peel and slice each banana lengthwise in half, then vertically arrange 2 halves, butterflied open, on each foil square.
Sprinkle bananas with chopped butter cookies and mini marshmallows. Fold up vertical sides of foil so ends meet, then roll downwards to seal the top. Fold in sides of foil to seal packets well.
Roast packets over a grill on medium, lid closed, or on a campfire grill until warmed through, 5 to 10 minutes.
Open packets, then serve warm topped with ice cream, sprinkles and cherries.
Tip
Packets can be baked in a 400F oven for 8 minutes.