A picture of my mom and grandfather. Everything else of real value is in a safe or fireproof lock box.
Your house is on fire but you're able to run in and save one thing. All people and pets are safe. What do you grab?
Mine is a crayon drawing my grandpa drew back in the late 30s/early 40s that my aunt gave me as a graduation gift. I had it professionally framed and matted a few years later, but before that I had it replicated in tattoo form. It is easily the most important item I own, though it's worth nothing to anyone outside of my family.