Check your brakes before you mount. The cables/mountings could be frozen in place and there could be ice build-up on the rims or brake pads.

Test your brakes occassionally during your ride home to make sure they work. Ice can build up during your ride.

Check for ice build-up on your derailures as well.

Read some of the winter bicycling tips in the "Winter Biking" section of BF.C.

Good luck. Ride safe.