Lettuce seed only germinates below 20 ° C ( 68° F) so avoid a position that is in full sun. Drying out can cause lettuce to bolt.
Sow some Oriental vegetables to use as cut and come again. They will be ready to harvest in a few weeks and good in salads or stir frys.
If growing salad crops in a container box or grow bag make sure it is deep enough to keep the compost moist at all times. If needs be, shade or insulate the container so it doesn’t dry out too quickly
Beetroot leaves look good and can be eaten as well as the roots. Try a few in a deep pot if you are short of space.
Onions shredded onto a salad are one of my favourites. You can pull young sets as spring onions so plant them close and eat as you start thinning out.