Get a box big enough to fit in. Then cut holes for your arms and legs. Then you can either paint or color or put white fabric on the box then draw paint or but black fabric for the dots. Don't forget to make different numbers on each side! Your head can be the middle for number 5 and stuff. Have fun trick or treating!
Thanks to Melanie for this fun idea!
For the dice(die) costume, it may be helpful to know that the numbers on
opposite sides of the die add up to seven. If you put on black pants or
tights or whatever, your legs would work fine as the two, then make your head
the center dot of the five by painting your face black and/or putting on a
black ski mask or toboggan. I just thought that might be a fun little
addition to that costume.
Thanks to Boris the Spider for this neat addition!