Thanks, folks, for all the helpful feedback! I've been trying to distill the vast amounts of information in the book into something that'll be useful during a game session, and your suggestions helped a great deal. Here's what I hope to be able to fit on the screen, in some version or another:
-The Resistance Table
-Resistance Formula (for whatever isn't covered on the Table itself)
-Spot Rules for Combat
-Spot Rules for Firearms
-Weapons Tables
-Environmental Damage (Falling/Fire/Drowning, etc.)
-Poisons (although this'll probably go if I need room, since I don't imagine it'd come up much)
-Damage Bonus Table
-Injury + Healing Spot Rules
-Combat Order Summary
-Insanity Summary
-Sanity Point Costs
-Temporary Insanity Chart
-Pronunciations of Mythos Names
-Vehicle Tables
I still have quite a way to go before I've got all of this in a form that'll be usable, but I'm pretty sure the list will only get shorter from there.
Here are some pictures of what we've got so far:
We're making the screen out of a couple of pieces of masonite board that we had cut to 7.5"x12", which is just a tad thinner than ordinary paper in order to save table space during use. Here are two pieces before painting.
My girlfriend Ally gave each board a coat of gesso and then a coat of Prussian Blue mixed with galkyd, which she tells me gives the smooth sides that awesome glossy textured look. The rough side of the masonite looks a little more muted in comparison, but that's the side that will be facing the Keeper, and it'll mostly be blocked by the charts.
Here is the (unfinished) painting that covers the four central panels of the screen. It still needs a few more non-Euclidean structures and some fog rising up from the sea, but I think it looks awesome as is. I may also have her write Lovecraft's couplet ("that is not dead which can eternal lie," etc) in gold paint just to set it off a bit more.
Here's the piece of leather with the gold threaded embroidery that will eventually be the front cover. We accomplished this by scanning the title page of the 6th Ed. book, reversing it, and taping it to the back of the leather so that Ally could trace it with the thread without the paper showing through.
As you can see, it's still a work in progress, but I think it's coming out pretty awesome thus far.
Any other suggestions that people have regarding the content of the Keeper's elements would be much appreciated, because as I said, I've never run a CoC game before.
Thanks again for your suggestions!