This would be super easy to make and wear. T-shirt, fabric paint (free hand or stencil) and chef's hat.
Black eyed peas [source]
Loved this characters on Sesame Street. Great couples costume! Maybe not so "last minute" but could be easy to do. Think towels, Styrofoam balls, hangers, and pipe cleaners.[source]
Who can resist a garden gnome?! [source]
Someone in our house should be this! Box, can of spray paint (any color) and bowls.[source]