I always think the best veggies to start off with are peas and beans, because they're so easy to grow, so useful (as long as you like them), freeze well and are quite pricey in the shops. Even with this year's horrible weather, I've got a freezer full of runner and French beans, in fact so many that those alone could keep us in green veg until next year's crops start coming in. Garden peas need a lot of space to give much crop, but mangetout don't and are very useful veggies. Curly kale and chard will stand and crop all year, so you get very good value out of the space, but only if you like curly kale and chard. Courgettes are tender and might not do well in a horrible summer, but most of the time they'll give you a huge crop for very few plants. I think it's nice to have a core of veggies like those that will reward you for your efforts and make you feel it's all worthwhile.
Garlic are also good value for space, I always think, because they're dead easy to grow, just about everybody uses them, and once you've spent a couple of years finding out which varieties do well for you, you'll never need to buy them again.
Tomatoes and cucumbers are so much nicer grown at home, but if it's a bad year for weather or if you're hit with blight, you might not get much crop. Lettuce are dead easy, everybody buys them and are so much nicer fresh.
And I'd get some fruit going too. Gooseberries, raspberries, loganberries, rhubarb, whichever you like best. All are very easy to grow, freeze well, and they charge a shocking price for them in the shops.
I think which varieties do well for you is something you need to find out with experiment or by talking to people growing near to you. It depends on the soil and the local weather conditions, so what does well for someone else on here might not do well for you.