I'd do a lot of the same, but in different ways. I don't want to mess up and miss out on my pets and all the other wonderful things that have happened to me, but I would try to live a better/less fucked life.
Try harder in school, achieve some modicum of success so I'm not such a loser, and fix my biggest, less consequential regrets. Nothing that would be life-changing, but would make me feel less guilty at least. I would do more to help the pets I couldn't save (2 babies taken too soon) and I would try to just live more, and not be as much of a shut-in homebody.
Probably try not to become an alcoholic too.