As somebody who goes on eBay a lot to buy old negatives, slides and amateur films to digitize and present online... much pre-WWII, I may be able to give some advice.
Make sure your archive is orderly.
With digital files, make sure the names are reasonable. Preferably, store on multiple different formats (Magnetic disc, optical disc, printed format.)
Add metadata such as date, location, subject, people in it.
As to picture formats no longer being supported... don't worry. I was able with a bunch of enthusiasts to decode my 1970s NASA mainframe tape reels. Pioneer 10/11 pictures on them, fun project!
We were only able to decode the 1970s data tape because it had a label with METADATA and CONTEX that gave us the info we needed. The data itself also had metadata.
For negatives or slides, pack them orderly. Have same metadata was digital.
What also really helps, is short notes written for individual photos of sets.
All of this will create interest in the collection because it adds C O N T E X.
To much I see auctions of just 100-500 random Kodachrome slides thrown on a heap and sold as-is.
Or people sell individual slides, removing all context that may have been there when it was in a set.
Everything. Weddings, kids, family reunions, parades, cars, fiancé. Grandparents. Pets.
Very sad.
Must have been cherished and important moments at one point.
I can't save them all ):