First buy a long sleeve black shirt, this shirt is going to stay as you bought it so it can be worn other times.
Next go to your sister-in-law's consignment store (if your sister-in-law doesn't own a consignment store you're more than welcome to go to my sister-in-law's consignment store) and buy a pair of black pants that are two to three sizes too small. It really helps if you find a pair with an elastic waist and your Pilgrim wanna-be is stick thin. Otherwise you may need to hem a regular size pair of pants.
Next borrow your older son's white soccer socks.
Go to Lowe's and try to buy a cardboard paint bucket. When you find out that they don't sell them go to two movie theatres and ask for a popcorn bucket. Feel really old and out of touch when the teenagers behind the counter look at you with dazed looks. Go through KFC drive-thru and ask for an empty chicken bucket. Try to do it with a straight face.
Place a paper plate upside down, center top of bucket on plate and hot glue in place. Let cool. Flip over, cut out center of plate leaving about 3/4" overlap. Then snip the paper plate at 1/2"-3/4" intervals and lay pieces flat against inside of bucket. Hot glue in place. Spray paint black.
Beg your family members for old black belts. Choose one, attach to hat and clip off excess.
Buy 1/8 yard of white felt, cut a shallow U shape out for the collar using your child's neck as a guide, attach a button and cut a button hole
Cut two trapezoids using your child's wrist as a guide, attach one button to one cuff, lose one button in the couch cushions, attach another button to the second cuff.
Receive an odd email from the teacher when you tell her you haven't started the costume yet. When your son comes home with a construction paper Pilgrim hat, say "oooohhhh, THAT'S what she meant when she said they could dress up like a Pilgrim or an Indian."
Relish all the hugs and kisses your little Pilgrim guy gives you.