Not a gun, but a guitar: a Gibson SG formerly owned and played by one of my heroes, the late Gary Moore. His son was selling it on Reverb for a price I could afford, but didn't think I could justify. I have since sold my old house (pocketing a ton of equity) and would never have missed the price of that guitar -- which, if I owned, would rarely leave my hands. I think of it often, as a reminder to seize opportunity.