Here's something I found a while back and have been meaning to post: it's Cal Jones's World War I draft registration card. (Click to enlarge.) No great surprises--I did learn what he was doing for a living in 1917, as he's listed as an oil pumper with a company called Corbin and Bradstreet (which I Googled to no avail). He enlisted on June 5, 1917, two months after the U.S. entered the war. For some reason, he (or whoever filled out the form) put down the wrong birth year--he was born in 1895, not 1896. But his age is listed correctly as 21.
I found this in an archive at Ancestry.com while I was taking advantage of a free trial there. Pretty cool. I'll try to post more documents and photos as I think of it; it's hard to find time for the longer, more encyclopedic entries, but I do like to put something up here from time to time.