This single Minion Eye from Despicable Me is great for a quick halloween costume. The pieces snap snuggly into place. i used 1in wide elastic as the strap. You'll need to sew one side of the strap on one side of the goggle opening. weave the other end of the strap through the strap adjuster. Then loop loose end of the strap through the opening on the opposite side of the goggle. bring it back to the center and sew it around the center post of the strap adjuster. You'll be able to easily increase and decrease the size of your head strap.

If you choose to avoid the adjuster, measure an appropriate length of elastic band and sew it to either side of the goggle.