Mid 40's and rain is prime hypothermia conditions.

Some thoughts:

In an emergency, plastic bags (trash can liners, walmart sacks, etc.) make serviceable booties. Wear them between your socks and shoes and your feet will stay warm. The vapor barrier will hold in sweat so your feet may get wet but they will still be warmhttp://www.gossamergear.com/cgi-bin/gossamergear/Mariposa-Standard.html. Tuck the top of the bags into your pants so water doesn't run down into them.

A Helmet cover is OK for short rides in rain, but does not prevent water from going down you neck, Better is a hooded jacket with the hood under your helmet. Just be careful you don't impact your side vision too much.