Mars: About Animals
Here's a little bit that Instapundit linked about therapy llamas visiting a nursing home. Llamas may not be the first choice to bring to Mars, but it still illustrates something important. We probably ought to plan on bringing a couple cats or dogs or have a couple of the individual "farm" animals in a petting zoo. Sharon Lee and Steve White, in their Liaden Universe novels have the concept of a "Pet Library" where people who live or travel on space ships can go and visit the pets.
So... two mental health issues... food variety (puddings, mayonaise, stew with meat, cheese), and companionship.
Materials production... feathers in a pillow, wool sweaters, down jackets, and moccasins, which I talked about before.
Lastly, and probably something I won't go into at length... medical research. If people are going to live on Mars and have babies on Mars, it would be good to have the experience and many generations of animal reproduction and development to study.