a big wool sweater, and wool scarf. and those fashionable fur covered girl boots. im a real animal out there.

i stick to the name brands...

in ALL seriousness.
-ESSENTIAL!!!!! patagonia breathable nylon style rain coat. I rode in a big rubber rain coat which wasn't breathable for far to long. We had rain constantly for over a week in WA this past summer, and besides getting just as soaked by sweat in the coat, the only other item i wish i had was a water-proof tent. both of which i have now . typically hood went under my helmet in the cold, and in warm i like to get my hair clean by leaving my head exposed. I also wear spectacles, so keeping them from fogging plays a role in my comfort. the shower cap idea is pretty good, or buy some silicone nylon and make a nice helmet cover, for it allows ventilation and as well to keep glasses un-foggy.
-post office issued gortex pants (not for warm weather, i prefer the spandex in warm rain cause they dry fast and dont feel wet, when wet)
- booties are the smartest item i brought with me, HOWEVER, i made mine to suite my clipless shoes, open footprint. That week of rain in WA, 8 hours a day of pedaling in rain, and then walking in the wet setting up camp, got my feet wet regardless (however always warm). We were stealthing it, so there was never a good chance of drying. full covered booties would had made this leg better than anything would had, wet feet for a week, swollen, sore, and itchy for two weeks after, suck. one of the reasons Im not touring clipless again is so i can wear full booties.
-paddlers cloves for when its cold. or any clove to keep a layer of warm water next to the skins. or waterproof gloves would be nice.