A few years ago I was in a bit of a funk around Mardi Gras and decided to go to a blowout Masquerade Mask competition by myself. It was very last minute, so I headed to Joanne's and essentially made my mask in my car with some super glue.
The headpiece I had already made (I added the peacock feathers last minute), but the base mask is just one of the nicer ones from the masquerade section at Joanne's with some stick on jewels and a short piece of home decor trim that I super-glued on the underside.
I ended up winning 1st prize! For anyone else looking for last minute Mardi Gras ideas, don't skip the kids' sections - they have lots of stick on jewels, stickers, feathers, and bows that are very easy to add to base creations and kick them up a notch.