I use both a helmet cover and a thin helmet liner when it gets cold enough.

For the hands, I go from fingerless gloves to medium weight fleece gloves (not cycling specific) to lobster-claw windproof cycling mitts as the weather cools. In very cold weather, I add thin wool glove liners under the lobster-claw mitts.

For feet, I'll use windproof toe covers down to about 45 and then full-coverage neoprene booties over cycling shoes.