What would I take if my house were on fire? I'd grab my dog, of course, and my "go bag," which contains the practical things that would be hardest to replace - documents such as my birth certificate along with a portable hard drive backup of all my music, photos, etc. If zombies were on the way, I'd get my go bag, throw in my purse, and the dog and I would be outta here.
(Maybe now you're wondering if I have a bunker in the back yard or five years worth of canned beans in the basement. Nah, I'm not a survivalist. I don't really expect zombies to attack me. (To any zombies reading this: I'm certain my neighbors' brains are MUCH tastier than mine!) But it doesn't hurt to be prepared in case I need to evacuate because of a natural gas leak or somesuch.)
How can I have a house full of stuff but no prized possessions? I simply don't get attached to things. It's not a choice, it's just my nature. In fact, I have trouble getting attached even when I want to.
How much stuff is too much? The answer varies by person. Some people are most comfortable in a Spartan environment.
Some people love to surround themselves with treasures.
So if there's no specific threshold, when does "stuff" turn into "clutter"? In my opinion, stuff becomes clutter when it becomes a burden; when it negatively impacts your life. When you constantly waste time searching for things, when you spend your holiday worrying that someone will break in and steal your stuff, when you avoid having friends over because you're embarrassed by your house... you have clutter.
I look forward to seeing other people's prized possessions and reading the stories behind them. :-) Thanks for the challenging yet fun assignment, Le Professeur Gothique!