You could add more leafy greens. Chard will grow in the cool spring and also the summer, when it's too hot for spinach or lettuce. Collards do well in hot weather. Kale is good in the fall, into winter. I plant rainbow chard mixes the most, because it does well in any season and is pretty, too. You can harvest just the outer leaves and have the plant growing all year. It even looks good in pots or flower beds, to me.
I always plant small tomatoes for the chickens, although they like large ones, too.
Some parsley. Chickweed. Purslane. A little clover and alfalfa. You can buy seeds for all of those. If you just want a small amount of alfalfa or clover seeds, you could buy a small packet of seeds used for sprouting, instead of the huge amounts sold for planting fields. My chickens also like sprouts. Like the other leafy greens, the chickens can just graze on any of these.
Really, any vegetable sold for people, although some may need to be opened up for them, to get it started. Then they can peck out the softer insides.
Pumpkins and winter squash are good in the fall and will store for awhile, too.
Any berry bushes would be nice. Maybe a grape vine.
