The Importance of Good Nutrition

I have heard it said a few times that a very important component of fitness is diet. I have come home twice in the last month very disappointed with my performance at the gym, because I was missing that good nutrition. I liken it to trying to demand high performance out of your car, and only using cheap gas. Sure the car / body will perform, but not up to it`s full capabilities. So the logical question, what does one do about getting regular sound nutrition? It`s not an easy question to answer when no one in the family likes to cook. I am open to suggestions.