My advice would definitely be think about what you'll want to eat! I ended up living on radishes, beetroot and spinach last year, and much as I like them I wish I'd thought about variety and quantity a bit more beforehand
Tomatoes are a good one as they're nice and easy to grow in growbags or containers and they form the basis of so many meals. I'm growing several varieties this year. I also think peppers are a good idea if you like them, mainly because they are so expensive to buy, yet pretty easy to grow! Although not sure how well they do without a greenhouse (I only have a cheap mini plastic one from wilkos, they're great if you're short on space but want to grow small amounts of peppers, chillis, cucumbers etc).
Also, a few shallow containers with mixed salad leaves are great as you always have something to go with your dinner, and they're so easy to grow! And herbs too, you'll find you use them all through the summer if you like to cook.