You can plant a row of Swiss chard at the same time. You will be surprised at the bounty. This spinach-like vegetable will produce prolifically into the first frosts of fall. Carrot seeds are tiny, and it is better to sprinkle these directly in the garden. Both carrots and parsnips will need to be thinned out when they are a couple of inches high, otherwise their deep pointed roots will not have room to grow and swell evenly.
Seed potatoes are available at garden centers and through mail order, and can be planted now.
Dig a trench at least 1 foot deep and place the seed potatoes at least 18 inches apart to allow the root system to develop the potato tubers fully. Cover, and mound slightly to prevent the roots from surfacing. Peas are a cool weather crop, and only do well here while our temperatures remain somewhat temperate. But what a treat it is to go out and pick some for the 4th of July celebrations. It is well worth planting them.