I got something like this and was able to get several out of one sheet. $12.50 w/free shipping

http://www.ebay.com/itm/12-x24-Blank...sAAOSwHjNV-1dV

I bought it in red but would actually advise getting some bright, obnoxious, contrasting color so you are more likely to notice you should remove it. Like Roger, I'm usually going down the road 30 mph before I realize I forgot!!