I feel a collaboration might be fun, so all your readers, let me know if you have an idea...
...the first one that popped into my head? I post a typical forgotten bookmark, and a few writer-types come up with a few paragraphs that might explain why that item ended up in that book. For example:
Postcard: Milan, 1961.
Dear Lover,It's over.-you know who
Found in "Catch 22."
"It was a dark and stormy night in Milan when I decided to dash off a final goodbye to that idiot lover of mine..."
You get the idea.
Let me know if you have any ideas, it could be fun.