Salad leaves would certainly be a good choice. Dont plant up the whole trough all at once unless you want to eat nothing but salad for a wekk then nothing at all after! Instead, plant a few seeds every few days, that way you will get salad leaves fresh as you need them.
Peas (get early varieties as they mature faster) Radishes Beetroot Parsley, basil etc. Spring onions You can probably buy small plants in garden centres still e.g. Tomato, chillies, peppers. Salad crops Mustard for cress That should keep you occupied.