There are quite a few versions of a small, flexible plastic mirror out there. Runs about $3 and can be found at outdoor stores such as REI, etc. Here's a link to it:

http://www.rei.com/product/710.htm?vcat=REI_SSHP_CAMPING_TOC

FYI - the Starflash 3"x2" mirror won't quite fit in my Lexan bottles. It's just a little too wide, by all of a millimeter.