Def for fruit: strawberries and raspberries and if you like blackberries you can get thornless varieties. Blueberries can take up to 3 years to fruit so you need patience with them.
You can get varieties of strawberries and raspberries that give you a crop from summer to late autumn so you can get a decent crop of a while.
With strawberries and raspberries once establishment you will never have to buy anymore plants as the strawberries will make runners of baby plants and raspberries will run like a bugger. (One of mine even managed to escape from it's pot and make new ones just outside!)
For veg this year I have had great success with the following all grown in pots: Peas, sugar snap peas, broad beans and dwarf french beans and even some pak choi. Also outdoor tomato varieties (remember to check they are OK for being outside) are great and easy to grow and mine have grown into triffid proportions with huge toms, just waiting for them to ripen!
Chillis are best grown in a greenhouse or indoors in a nice sunny position (I've got a plastic walk in cheapo greenhouse I got a few years back for about £30) and mine are flowering now under the mutated indoor tomatoes. 
Lettuce and oriental cut and come again are easy to grow but can bolt very quickly.
Basically what fruit and veg do you like to eat?? This year I'm growing things I know I will eat.
Mint def needs to grow in a pot or will take over your garden. I have a bay and rosemary growing in pots (they seem to love being root bound as well so you only have to re pot them up every few years).
And also don't panic if things don't grow or die. It just means you have new space to grow other things 
Oh and second trees in pots... just don't bother... stick them in the ground.
Also check out some online seed and plant shops and order a catalogue from them to see what they sell.
You can spend HOURS going through them and making wish lists and using that to do additional digging around on the internet on what you fancy!!! (I do that with a nice cup of tea and biccies.. lovely way to kill and hour or so)