To start getting these pictures into their long-term homes, I ordered an initial round of storage supplies from Archival Methods. These include tissue paper, a big 11x17 box for some of the oversize prints, a smaller box for 3.5x5-inch prints, 500 print sleeves, a number of open-ended paper envelopes, and index divider cards. While this certainly won't hold everything, it is a start. I think I'll probably be placing a monthly order for at least the next few months.
I also ordered 50 gold DVD+R discs. They are relatively expensive, four or five times the price of Taiyo-Yuden DVD+Rs as sold under the Verbatim brand. Because the gold reflective layer does not oxidize like aluminum, marketing materials claim that they can last 100 years or longer. Some gold CD formats even claim 300-year longevity. That seems unlikely, and even if they survive for 100 years, consider: how many 100-year-old media formats can you use today? How many 25-year-old media formats?
Still, my hope is that they will last long enough for a member of another generation to explore. If that person is smart, perhaps they will copy the files onto some undetermined future format and create their own distributed backup for yet another generation.