at that time of year i plant/sow:
onion sets
garlic
spring cabbages
peas 'Feltham's First' (under a cloche)
hardy lettuce (under a cloche)
mizuna (under a cloche)
lamb's lettuce (under a cloche)
spinach (under a cloche)
hardy annual herbs
if the ground isn't to wet/cold then you should plant any fruit trees/bushes at this time too and also rhubarb.
you can also sow broad beans
oh you are going to be so busy, but this is really the best time to get an allotment so you can clear the soil, make beds and manure the ground before the really busy time starts in spring. don't try to do too much at once, concentrate on getting your perennial weeds under control first, that's a winter long job in itself usually. but most of all ENJOY YOURSELF, it's all good fun, and besides, there's always next year!