Have a look at what the other plot holders are doing, especially some of the old boys who have been there years and done it all.
I grow all the high value crops I can, but have 3 allotments and have space to leave crops in that take time to mature such as broccolli etc.
french, runner, borlotti and broad beans all go in. Toms I grow are F1 Ferline as more blight resistant.
Loads of squash and pumpkinns, globe artichokes, parsnips and carrots, elephant garlic, onions and shallots, loads of leeks and caulis, sprouts.. all sorts
sweetcorn fresh off the plot is the best you’ll ever taste. Asparagus is great if you have room to out in enough crowns to get decent crops, but it does take a lot of room and time to mature.
When you are chatting to othor plot holders down there there may be some Rhubarb crowns that are being given away and shared, also soft fruit cuttings available are a lot cheaper that buying all your own stuff.
Only thing I dont grow down there is peas, I grow sugar snap and mangetout , but peas are cheaper and just as sweet from the tesco freezer!