Number one item which HAS become merely an historical relic:
The Sliderule.
Back when I was in College it was a required item. I had a really high quality one. Now.. A sliderule is totally a museum piece.
Curiously, the Abacus is still popular in Asia.
Then rotary dial phones. And Pay phones are becoming rare too.
I believe you are wrong about books though. It is a hobby form, and will remain so. One store is doing VERY well during the resession and that is Half Price Books. They are still doing a big business.
Though the public library is becoming more of a "Book Museum" sort of place. Only the use of public access computers keeps most of them filled with patrons. A few people still borrow books, but the old way of students cramming the library to do research work is definitely gone. And the borrowing of research materials is now around zero. All the stuff is only popular consumption. Novels, Mysteries, Cookbooks..
One great thing about the internet is the availability of anything you ever wanted. Used to be if it was not sold at a local store, you were S.O.L. on it. Now, you can buy stuff from all over the world.
Whatever you might fancy, you can have it. Obscure, no problem. Rare, no problem, just you may have to pay plenty!!
Music. Used to be all you could buy was what happened to be at the local stores. Now, anything is available.
I have been buying from Amazon, and have to say being able to find the very best selections, and at a low price is fantastic. I still buy CDs. And can say my collection is top notch due to being able to find the stuff i really want on Amazon. (I am lucky I also have four really great local used stores to buy from.. but as i said, there, i have only the limited selection they might have on hand)
And I do not think music is endangered. i think it is changing, to a computer based distribution system, which will leave out the fossilized majors.
As for other things that will disappear.. Well insects are gone. Used to be insects everywhere in the Summer. Now, damn there just are none. No butterfly, no wasps, no bees, no dragonflies... Strange shit is happening to insects. At least where I live.
Then food. I think food is the next big crisis. Soon it is going to be the most expensive thing. Maybe not for a few more years.. But just wait. Soon enough we are going to be paying the major part of our income for food. My prediction as you will. by 2020... you are gonna be sorry as hell over food.
Food Riots. Supermarkets are going to have hundreds of people converging on them. fill up baskets and leaving all at the same time. They will also trash the stores while doing so. Teargas, riots, cops shooting folks over food.
Just a few gigantic companies control 99% of the worlds food supply. Eventually they are gonna figure that out. And the greed is gonna take over. Look at Monsano.. they have the seed crop cornered totally. Anyone else has been squeezed out of business due to GMOs, and the pollen problem (pollen from GMOs pollute nonGMO,and then the non GMO get sued by Monsano for using thier stuff without paying!! true!!). Since the laws back Monsano 100% we ARE screwed as human beings.
(My last prediction came true. I remember telling a friend as we rode the bus to work back in 1983 Just wait, folks will be shooting each other for no reason, just walking down the street and shot dead. That has come true. big time. (at least in the inner cities.)
For the rest who cares. Things change. I am old and will be dead in around twenty years.