Experts and BHG readers answer.
Many vegetables come back from seed. Only trouble is the varieties don't come back true from seed. But if you don't care that much about whether the varieties are exactly what you started with, then just leave some of the old ripe fruit or seed heads in the garden at the end of the season and you will have plenty of volunteers. I constantly get tomatoes, peppers, dill, fennel, cilantro, coming back from seed.