I am thinking about ordering slip on, clear plastic covers for all my shelved hardcover books. Currently, they are bagged and shelved.  I have a smaller selection that is boxed which are fine bagged. But, I find it slightly annoying to have to open and close the bags each time I want to access a book of the shelf. I might want to reference a page, and it takes me longer to get it and put it back than to read what I'm looking for.  So, I found some 11 1/2" x 21" covers. Can someone check the dimensions of their 1st edition hardcovers. I believe they are 11 1/4" tall but not sure on the length when fully open, maybe 18 or 20 inches?

I was looking at these: For Sale, Adjustable Book Covers Fits 11 1/4 inch Tall Books, Polypro

Cool. Let me know what you think.

I was also thinking of using either 2 or 3 inch 3-ring binders with 8.5 x 11 sleeves to be able to shelve and access the modules and thin soft covered items. My only worry is that they'd slide out the top if not careful...

Good idea, the Ultra Pro card binders have a band like that. I think side loading sleeves would work, just a matter of finding the right size since they seem to be made for either comic books or for business presentations that only hold a couple pages in each sleeve.

EDIT:
Here is a video of how the book covers work and adjust to fit. Clear Book Covers - Adjustable Width - Disposable Clear Sleeve Protection - YouTube