You can extend the growing season by covering your plants with those 55 gal contractor trash bags at night. If a frost advisory/warning is in effect for a given night, just cover the plants in the evening/afternoon and then remove the covers in the morning. I think it also helps to lay some black plastic around the base of the plants. The black plastic will pick up and hold heat from whatever sun there is and release the heat back at night.
This applies to a soft frost, where the temp might hover around freezing or just below it. For a hard frost, I guess it's just harvest whatever you can.