Hi All!
Most of this was covered, but heres another 2 cents. Maybe it will help.
I have a little experience artwork preservation/conservation kinda stuff. I collect a lot of very old papery kinda things.
With paper, if you're going to store it, have it between two acid free rag mats. The mats can be hinged with acid free tape. The artwork/signature can even be hung inside of these using an acid free type of rice paper and acid free tape making a kind of pocket to put the artwork in inside of the mats. Store it flat.
Another way to store paper based art is to put it in an acid free folio. This isn't as good as the mat solution, but the artwork is always available for viewing. These are available on ebay and elsewhere for a reasonable cost. They come in different sizes and are acid free. You have to pay attention how you handle and store the folio, since the items are loose in them.
The best way I have found to store paper based art is to frame it. Being conservation framed will preserve it and you can look at it. Acid free rag mats, UV glass, Acid free backing(no glueing/dry mounting

), any good conservation framer shoould be able to do it. It costs more, but it is worth it. Take the art off of the wall once or twice a year to make sure the backing is intact and no spiders or other things are trying to live in it.
As far as objects, especially plastic ones, it's pretty much the same as paper. No direct sunlight. No Smoking. No Dust, no, no,,,, The best thing I've seen is to keep it in a sealed box and take it out when you want to look at it, and never shellac or coat them. That stuff deteriorates over time destroying the sig and the object. An arcyrilic case or a trophy/china cabinet with a UV glass front works good too.
I keep my paper stuff framed or in a folio now. My plastic kinda things go into a box in the closet or are displayed in a closed cabinet.
Here are pictures of two different sized folios I use. They cost between 15 and 45 dollars. Here is a picture of a conservation framed etching. It cost around 200 dollars to do it. You can spent less if you use one mat and a metal frame.
