Here is a subject that's near and dear to me, makeup. OK not traditional make up but special effects makeup, radical stuff like prosthetics and the like. Anyway the problem is in being able to apply something in the field in under 5 minutes. You should be able to carry it in your pocket and conceal it easily.
The only thing that I can come up with that wouldn't take years of training would be rigid colodian also known as scar liquid. Basically it's plastic in an ether solution so you can paint it on your skin, it dries in a minute and you can create instant scars. More than that you can create a large acid burn on the side of your face in a matter of minutes. It comes in bottles a little bigger than a nail polish bottle. It's also fairly inexpensive.
It does look a tad shiney though but I don't know if the eye in the sky will pick that up. Anyway would this have a chance in defeating facial recognition?

