I've heard too many horror stories recently. People didn't plan for their family papers and photos. Descendents have sold them to antique stores or on Ebay. Some disappear forever.
I've been relatively lucky. Most of my ancestors handed items down to people they knew would care for them. A few were more proactive. One of my ancestors donated her family papers to the Connecticut State Library. Another donated art to a local museum. In doing so, they ensured the items were to be protected. And, as I remember often, they also made sure the items would be available to me when I wanted them - as well as to their other descendants.
So, while I'm being thankful, I try to remember to plan for my own collection. What will I do with my papers? Hopefully it won't come up for a long time, but it never hurts to be prepared.