Lots of good tips already. Here's a couple of add-ons that may also help:
Food before bed is great. Sugary hot chocolate gives you an immediate burn, but I'd accompany it with a longer burning protein to keep you fueled into the wee hours. Nuts are awesome for this. Cup o' hot chocalte with some nut butter on bread, or skip the hot choc-ey and go for hot herbal tea with a handful of chocolate covered almonds or similar. 'Course, a smokie on a bun would do the same thing, but often that's a less enticing treat before bed.
Getting the blood flowing is also a really good option to generate body heat. More body heat equals a quicker heating of the air in the sleeping bag which ultimately equals a warmer, happier you. I would suggest getting the larger muscles groups involved, especially the quads. A brisk walk if the terrain allows it is good, even better if you throw in some lunges or squats or step-ups. The nice thing is that even with a small beach and thick underbrush lunges and squats can still be done. Step-ups too, if you find a dry log, flat rock, or the right root-step. Flap your arms about at the same time (you can make this less silly seeming if you want :lol: ) and you'd be surprised at how quickly your body temperature rises, even if you're squats are more bends.
And dry is key. Having just completed one of my wettest trips ever, matched only by a winter ski trip that halfway thru became a spring rain and slushfest, I can echo the others who've stressed the importance of clean and dry. Once the weather turns wet I keep a sleep-only, dry at all costs outfit on the go. I can stay warm and damp while awake with proper hydration, feeding and exercise, in addition to the right clothing, but my sleep is a whole lot better if my body can just shut down and recharge without fighting damp clothes (or a damp sleeping bag for that matter. I also pack my sleeping bag into it's drybag when I am not actually inside it to minimize picking up moisture from the environment). I also *try* to stay dry during the day, which is sometimes easier said than done.
And finally - if you are lucky enough to do a trip that is dry (hooray!) but cold, then the key I have found is to never allow yourself to get chilled in the first place. Remember that keeping yourself warm is a huge energy suck, even if you aren't paddling hard. Eat and drink lots and never allow the internal furnace to go out. Put the toque and the extra layer on when you stop moving to keep that heat in. Sat still long enough to cook and eat? Time to get the blood flowing again - think of it as adding oxygen to the fire. Run (briskly walk) a relay race to the water with each separate dish as you clean up after dinner. The trick here is to keep moving enough to keep the muscles warmed up (and warming you up) without exhausting yourself. So now is not the time to put marathon training into action but is the time to maybe walk up and down the beach a few more times than is necessary with some deep knee bends or an aproximation thereof at either end.
Good luck.
The hot drink didn't work too well either as I had to get up several times in the night and lost all my heat in the process.