Mice will not bother your gear that is not associated with food. Their sense of smell is way better than humans. You can keep your gear in your pack or in your tent, it doesn't matter.
As for the 50 foot rule: 5 or 10 feet works for me. If it is really bear country, I tie a bell to my Ursack, and tie it to a tree at a distance where I can throw rocks if an animal does bother it.
