For food, just read the ingredients on the bottles and look for something that is mostly meat rather being full of corn or other veggie filler. Check out NLS and Omega One.
For plants, that is a very long question. I suggest doing some more research into plants. Just figure out what sort of lighting you currently have. Some easy ones to look into are the Java fern, Java moss, and Amazon sword. Those will grow for most people under most tank lighting. They keep the water nicer and give fish places to hide. They also are easier to kill than the plastic ones. If you are able to keep plants, I always suggest at least trying out something very basic like the ones I suggested or something similar. If you do a search for beginner plants or low light plants, you will get a bunch of ideas and then check out those individually.
Hope that helps.