Busted eyeball
All you need to pack for this “eye-catching” (sorry) costume is a ping-pong ball attached to a bit of yarn and a bandage.
Paint the ball to look like an eye and dab a bit of glue on the back. Glue on several short pieces of red yarn, then braid the yarn, giving the appearance of an attached optic nerves. Tape the end of the braid into the inside of the bandage, wrap the bandage around your head so that one eye is covered with the fake eye dangling beneath, and voila. Gross.