In the USA, at least, you can now read/search online and download as a pdf:

July 1944 Air Forces Manual 21: Survival On Land, At Sea

Nothing earthshaking here, but since Google Books went to the trouble, I thought I'd advertise it.[1][2]

One still-pertinent item is this tutorial diagram: Sighting a double-sided signal mirror

(The aimers in the signal mirrors stocked in oceangoing lifeboat kits are overwhelmingly
the inexpensive double-sided or foresight aimer (aka heliograph) type, rather than
the more effective retroreflective aimer type, so it is good to know all three signal mirror aiming methods.[3]
(All are more accurate than the improvised "vee-finger" method, which is a particularly iffy variant of the foresight method).

The bibliography entry for this item is:

Survival on land, at sea ; prepared by Arctic, Desert, and Tropic Information Center.
[James Gray, Inc., New York, N. Y., July 1944.]
[2] +78 p. il. narrow 12° (Air Forces manual 21.)
[Pages 75-77 are left blank to be used for log.] W 108.19:21

The downloadable pdf is "image-style" (non-searchable) version, but you can search the online version.

[1] I had noticed that Google Books had this set for "snippet view only", so I requested they review it for unrestricted viewing in the USA (may still be blocked outside),
and they did. Since I put them to that trouble, I wanted more folks than me to benefit, and it seemed like something of interest to this forum.

[2] Other copies on Google Books:
https://books.google.com/books?id=QoNYtQEACAAJ
https://books.google.com/books?id=ILDe_J2czBMC

[3] Training videos for the three types of signal mirror aimer:

Double-Sided Signal Mirror Aimer:
(fancy version here, but simple steel plate with hole is aimed the same way):
The Signaling Mirror: WWII US Government Training Film

Foresight/Heliograph Signal Mirror Aimer:
Using a foresight signal mirror aimer

Retroreflective Signal Mirror Aimer:
Using a retroreflective signal mirror aimer, red-dot subtype

Awesome! Thanks for the heads up!

interesting document. While some things have changed, much remains the same.

I was particularly interested in the section on dealing with "natives." It reads like an intro to a course in cultural anthropology, although isolated "native" groups are hard to find these days....