Tomato blossom end rot: (usual cause: calcium deficiency)
Grind some eggshells in the blender with water. Pour this mixture around the plant, and water well. Won't cure the present rotted tomatoes , but you might save the next fruiting bunch if you take swift action. I save my eggshells all year long, let them dry in a pail, then crush them by stepping in the pail, then add a handful to each hole when planting, and also some at the top of the soil. Works wonders.
Lettuce plantings: Successive plantings can be made every 10 days apart for fresh lettuce up until heavy frost. Lettuce is quite hardy. Some varieties bolt easily, but I've seeded lettuce at various times in spring and summer, and it was usually one of the last plants to freeze.