Licking the A-B-C's

All I want for Christmas is a three-cent stamp. A paraphrase of the old song comes to mind as the Postal Service announces a 2-cent stamp just in time for the holiday rush -- and as we recall the man at the post office the other day who asked absent-mindedly for "a book of threes, please." He was probably of the generation that remembers "C" rations and "K" rations, too.

Let's see now was it K that meant a solid packet or rations for one man and C that fed five men for three days or three men for five days -- or vice versa? Or something else entirely? Will someone of the current alphabetized generation run across a purple "B" postage stamp someday and wonder if it really referred to 18 cents as we all know now? What about the brown "C" that is already prepared to mean 2 cents until the stamps marked 20 are available? Quick now, what did the "A" stamp mean? Or was there one? And will "D" mean 25 cents or be rounded off to a dollar?