It is a good idea to go for plants that normally cost you most when you do the shopping.
I haven't grown Rocket in a container, but it's a good thing to grow if you like it - you can pull a few leaves at a time and even save seeds for the following year. The flowers can also be eaten and have an interesting, slightly differently peppery flavour to the leaves. You can keep the plants growing right through to winter - chop a couple of leaves finely and sprinkle on the top of soups.
You can get mixed salad leaf seed assortments which may be good. Sow thinly and offten - pick young.
If you use fresh herbs, such as basil, corriander or parsley they are worth growing - I used to have a couple of parsley plants in each of the hanging baskets outside the door - easy to grab a sprig when needed.
Peppers would be a good candidate, but are not always successful. French beans are easy 1/2 a doz in a big pot should be OK - once again pick young and frequently to keep them cropping.
Remember that, in containers, they need frequent watering - you may lose plants if you go away for a few days when it is hot.