As the previous poster noted, a hot meal and a hot drink do a lot more to keep you warm and happy than the best gear in the world. If I am going to be in the cold all day I always eat significantly more than normal and eat frequently. Always keep your bladder empty, a full bladder is a cold bladder! This is doubly true at night!
Everything below is minor in comparison to the above....
Always keep your feet, neck, and head warm! Even if they do not feel cold, put a layer around each anyways and you will stay warmer longer!
When riding, stop 100% of the wind and do it away from your skin. This is far more important than any heated gear or insulation. Winter gloves are NOT sufficient for this, add a rubber over-glove! I recommend rain-off gloves because they combine fingers into 3/1 or 2/2 mittens for extra warmth. Do not underestimate the power of heated grips, I can be comfortable far below freezing with heated grips as my only heated gear.
Get a good down sleeping bag and a silk liner. Do not skimp, expensive bags are worth the cost if you are in cold temperatures. Remember the standard wisdom of dressing in layers when outdoors still applies. The tent with its fly are your first two layers. Your bag and silk liner are the next two. Keep all of these as small as possible to do the job and you will stay a lot warmer. You will be warmer in a ditch in the snow with a tarp than in an over-sized tent!
Get an Exped Downmat for beneath you. Best pad ever.
Wear a warm hat at night. Wear warm socks at night.
Always have a set of chemical hand-warmers just in case. Spend enough time in the cold and you will need them sooner or later.