"My Confession: Recollections of a Rogue" by Samuel Chamberlain. Sam Chamberlain was one of a kind. Born in Massachussetts, he went to Illinois as a boy and while still a teenager joined an Illinois regiment that marched to the US-Mexican War. In San Antonio Chamberlain joined the US Dragoons and fought at Buena Vista and other battles. His is one of the best first-hand accounts of soldiering in that war, and he had very wide interpretation of "soldiering." Sam considered himself a great hand (or other bodily parts) with the senoritas and tells of being in bed with two Mexican sisters when their boyfriend intruded. The boyfriend attacked him with a knife but Sam got to his sword and cut him in such a fashion "as to render him of no further interest to the ladies."
After the War Sam joined with John Glanton on the famous scalp-hunt of 1849. His account forms much of the source material for Cormac McCarthy's "Blood Meridian." This is the sole source for the character of Judge Holden, the villain of McCarthy's book.
All that said, one must take Chamberlain's account with a bit of salt, as he was known to tell some stretchers. For instance, he writes of his experiences at the siege of Mexico City, but in fact he was in a hospital at Monterrey when it happened. Nevertheless, it's an excellent account of the battle and he clearly interviewed many men who were there. He had distinguished himself at the taking of Monterrey. For all his bombast, Chamberlain was the real thing. He re-upped for the Civil War, rose to the rank of brigadier and was wounded six times.
Best of all, his account is profusely illustrated with Chamberlain's own art. He was a self-taught artist and it shows. But he had talent and was a keen observer. If you want to see what people of all walks of life wore in the US-Mexican war, check out Sam's pictures. It includes the only known likeness of John Joel Glanton, portrayed luridly in a barroom in San Antonio, dressed in full charro fig, standing over a slain victim with a bloody bowie knife in his hand.
Some years ago a Texas press put out a coffee table reprinting of Chamberlain's book. It is very hard to find now, and very expensive. I wish someone would reissue it. For a sampling of Sam Chamberlain's art and writing, check out
http://tshaonline.org/supsites/chamber/What I would not give to meet with Sam Chamberlain in retirement, sit down with him and a bottle (or several), and listen to him speak of his fantastic life.