What do Worms Eat?

We took the worm farm to our place, planning to transport it to a friend's house when she is ready to take it. She is a gardener, and can therefore use the compost the worms prepare and their waste matter to fertilize her plants. But she hasn't answered the phone; I fear she is out of town, and am not really sure how to take care of the worms while we are waiting for her to come back. I took the worm book my father used to learn how to care for them, but we don't have the little food processor he used to grind garbage up for their meals. I will have to use a regular food processor to grind potato skins, eggshells, and whatever else comes up. Not everything is appropriate for the worms; I know this much. They like watermelon rinds, but not citrus. Coffee grinds are good, but no one around here drinks coffee (except instant). Perhaps tea bags will work, if we chop them up, but it will be herbal tea, and some of that may be citrus. He told me a little citrus was okay. We don't have as much garbage as the house did. They had many more people after all than we do, with just the two of us.
I am afraid I will kill my dad's precious worms. I know he worried about leaving them.