You need to encase them in something or the inks on computer print outs will fade (And they may anyway, as computer inks are comparatively transient). You can buy protective containers to encapsulate paper stuff.

If you're under time pressure, at the very least take a Sharpie write a message about yourself, the world, the weather today, who lives in your house now, even the names of the carpenter and the cost of the work.

I was painting my house in Virginia on the morning and afternoon of Sept 11th, so I wrote a bit about that awful day and what was worrying us all high up behind a shelf in a closet. It helped a bit to leave some small record, and maybe someday it will be interesting when someone finds what I wrote.

I always leave little notes when ever I make a change in my 160 + y.o. house, with names, dates, reason for project, and often costs. I know I would be thrilled to pieces to find this kind of evidence, so it's the least I can do!

Molly~

.Mine has alot of history as a col.Himes in battle of gettysburg owned this house.So I put all I know,copies of deeds,I put 1 each of our currency,pictures.a letter about all we did here,I put it in container and put it in the wall.
I also did this to my past house that we built and lived over 20 years.Can you imagine finding that many years later.That would be exciting.

My DH had to replace some drywall in our DR, so my son (9 at the time) made a small time capsule. He put it in a ziploc bag and DH nailed it to a stud. He put in a note with his name, a Hot Wheels car and some other small toys. Who knows???

Those bookcases when filled will add lots of weight that must be transferred to the earth beneath the house. Is all well structurally?

Oh, yes indeed. The old place is solid as a rock.

And the bookshelves are beautiful! They look like they've been there from the start. Now I feel ashamed of all of our old beat-up books! Time to start buying leather-bound classics, I can see that.

Here is a link that might be useful: Beautiful shelves