Gosh...quite a few.....potatoes for a start....broad beans....onion sets....depends what you want to grow....check the back of seed packets at the garden centre......

The way the weather is going at the moment we will be lucky to start planting by April! In a year like this I would be very wary of the advice on the back of the seed packets - use common sense.

Seriously depends on the weather... Then if you are following the moon guide you need to check what to plant when... Right now, so far as we are concerned - big fat zero as the ground is frosted and we have snow - again!

Don't be too quick to plant any veg seed, if you plant a little later the growing plants will easily catch up given they are sown when the weather is warmer

And take a look at the blog I just posted for what to plant when in March

I'd recommend mizuna greens as you get a lot of tasty leaf in a very small area which you can cut and leave to come again (eat it raw or cooked like cabbage). I'd also recommend the small white turnips like Tokyo Cross or the little long ones like De Croissy. These grow very quickly and are sweet and delicious.
With a little warmth, you can get beetroot growing in modules, ready to plant out as soon as it warms up, as planted very closely these will give you delicious baby beet in the late spring.
You'll find all of these things do better if you start them in modules and plant out the tiny plants though, as they will germinate better and you can get the spacing much more exact without any waste of space.