I'm a carnivore, and I honestly would have trouble never eating meat again, so animals for food isn't something I really have a problem with. To be honest, whenever I've seen a movie where humans get eaten by aliens or hear a story where a person is eaten by a shark or a bear or some shit, I kinda just think "Well, food chain." We do it to other animals, so to be outraged or horrified if another animal does it to one of us is hypocritical. As long as it's done in a fashion that doesn't promote unnecessary cruelness or suffering, I don't condemn the consumption of other animals.
But if we're going to use them, we should at least be responsible about it. I don't mind leather, because we eat the cow anyways. Clubbing baby seals over the head for their skin, cutting the fins off sharks and throwing the rest back, cutting the tusks off elephants, etc. I don't condone shit like that. Hands off the endangered species too, we don't need anything from them that badly that we can't get from somewhere else. We may be the top of the food chain, but that comes with responsibility. Otherwise, we're no better than a virus that's wreaking havoc on it's environment.
Science is a gray area. Well, medical science. I don't condone use of animals for cosmetic science, but while I don't like the idea of animals being used for medical science, I can't deny the benefits of all the knowledge gained, knowledge that's been used to save other animals as well as humans. Besides, the knowledge gained in medical science hasn't been all from animals. If you look back on medicine way back at the turn of the century, they had all sorts of arcane ideas that were used on humans, and we learned from those too.
As for pets, treat them right. Neglect, abuse, using them for fighting.... that's just sadistic and irresponsible. I see pets in a similar light to kids. If you can't take care of one, or if you're going to get one for the wrong reasons, then don't even bother.