The older I get the less interest I have in riding brevets in the freezing rain, but here are a few things I have tried in the past with varying degrees of success:
Neoprene sailing gloves
Neoprene socks
Wool socks
Waterproof insulated hiking boots
Waterproof insulated cycling boots
Gore-tex overshoes
Gaiters
Gore-tex rainsuit
Thermal bib tights
Thermal jerseys and base layers
Some combination of those thigs is the best you can do, but I don't think there's any way to stay warm all day when it's in the 30's and raining. There's going to be some suffering.