Found this relic while I was looking for something else.
The M1 Radiac calculator, which produces your expected radiation dose, given the reading from a Geiger counter or one of those, the elapsed time since the bang, and how long you’ll be exposed:
If you’re a belt-and-suspenders type, you might carry a dosimeter, too, which calls for a homebrew charger or, better, an official one.
The M4 Nuclear Yield Calculator which, according to those Official Instructions [Update: dead link], gives incorrect answers and has been replaced by the M4A1:
They’re basically circular nomographs, made from stacked plastic disks, with various index lines and notations. You could use the flat nomographs with a ruler, but what’s the fun in that?
All inside a vintage plastic pouch:
Some of the stuff around here, well, I hope I never have a need for…
[Update: That comment there has a link to a DIY version. Go for it!]
The Smell of Molten Projects in the Morning 
The M1 Radiac calculator would be handy as an iPad app if the gizmo were EMP resistant. A nice rubber costume is a must, gives street credibility…
http://janoinen.net/smff/index.php?topic=4160.0
Right up until the battery goes dead… slide rules FTW!
But if I had a doggie which would be equipped with an outlet…
A gasoline-powered pooch!
A light mortar rhythm section uses also a “slipstick” + graph paper and a map to fork the shooting parameters.
http://en.wikipedia.org/wiki/81_KRH_71_Y