Lesson learned, for all the good it does me.

Do not store stuff in plastic trash bags in your hot attic (the kind of attic you crawl around in). When you want to see what is in the bags 40 years later they will have turned to messy plastic fragments. Cardboard boxes don't fare all that well, either. Think twice or thrice; do you really need that stuff you're putting in the attic? I realize most of you won't be living in the same house 40 years later, anyway.