You can grow anything and everything that you may fancy. It is still sowing and planting season for many veg for outdoors and your tunnel will extend the summer and allow you to grow stuff that little bit longer
I would not start tomatoes from seed anymore but if you have plants...or if you take cuttings from somebody else's plants, you still have good change of getting fruit. Tiny tomatoes...those that are for containers and baskets you can still sow.
It all depends what you want...
If you get hold of some strawberry runners...pot them up and/or plant them in tunnel..you can grow strawberry plants outdoors during the summer but take them in for winter and they will start flowering for you early next spring and fruit far earlier than plants outdoors
You can get some basil growing between toms..and/or salads?
