Wear a toque at all times, esp. at night.

Dress in layers. Remove layers when required to keep from sweating. Sweat = wet, and wet=cold.

Wool or fleece are warmer  than cotton and nylon.

Nylon outer layers are good to keep out snow and ice

Leave the bug spray at home for this trip.

Eat lots of high-carb foods. Winter camping REQUIRES 5000 calories per day.

Drink lots of fluids.

Bring a chair to sit on.

A foam cushion will help keep your tush warmer when seated. Closed-cell foam works well for this (carpet underlay)

Alcohol might make you feel warm, but since it promotes perspiration it will actually lower your body temperature. Be VERY careful when mixing alcohol with cold weather camping.