Make a snowman out of marshmallows
Marshmallows, large jelly sweets eg Fruit Pastilles, strawberry laces or similar, Smarties, small skewers, writing icing. Sandwich bags and labels to take them home in.
Stick two marshmallows on the skewer and top with a jelly sweet for a hat. Wrap a length of strawberry lace around the middle as a scarf. Draw on a face using writing icing and stick on Smarties as buttons.
I got the jelly sweets and laces from Poundland - one pack of each was enough for a group of 26.