What can i plant now.....

calabrese Samson is a good one to plant now. You could sow spinach Bordeaux (but not too much as it's rampageous, lovely stuff though)
heat treated Japanese onion sets, shallots and garlic can go in now, and brassicas such as spring cabbage, cauli and kales

Heavy clay soil likes a bit of manure, grit or sharp sand, spent grow bag compost etc, home made compost and leafmould. Any organic matter is good for clay.  As soon as the weather allows you could plant potatoes as they are good at churning up the soil, as are leeks and celeriac

I save all my leaves from home and put them in a wire bin I made at the lotty.  These eventually rot down and make crumbly compost-like medium which you can incorporate into your soil or into home made compost.  I add it to my carrot beds too