Cover them---cardboard boxes, sheets, towels, newspapers, quilts, anything.
It does not take much to stave off a degree or two of frost.
Thin plastics are not as great as heavy paper bags etc., but plastic pails and bins will stave off light frost.
Also water plants well the night before.
Jugs of water placed near plants, and covered with plants, will act as a heat sink and protect through light frost.
