Portable soup
from http://www.foodtimeline.org/

Portable soup (aka "pocket soup," "quick soup," or "cake soup") was consumed by some early explorers/settlers of the New World. It was light in weight, simple to transport, easy to cook, nutritious, and filling. This particular food traces its roots to 17th century Britain. Lewis & Clark were famous for stocking mass quantities of this particular item to ensure their expedition crew would not starve. This is what the food historians have to say:

"With the vogue [late 17th century] for thin soup based on chicken or veal broth came a new invention. Its earliest name was veal glue', and it was the forerunner of the bouillon cube. Strong veal stock was slowly stewed for many hours, strained and simmered again, allowed to set, scraped free of sediment, and then gently cooked...It was a great deal of work for such a small output. But veal glue, its name later changed to 'pocket' or 'portable' soup, continued in demand all through the eighteenth century. Jam or beef or sweet herbs were now often boiled with the veal, to give a tastier flavour."
---Food and Drink in Britain: From the Stone Age to the 19th Century, C. Anne Wilson [Academy Chicago:Chicago] 1991 (p. 224)

"Portable soup
a product which achieved some prominence in 18th-century English cookery books, was a precursor (and a relatively sophisticated and refined one) of 19th century Meat Extracts and 20th-century stock cubes....Hannah Glasse (1747) gave two recipes, one lifted from an earlier work...Both state that a piece of the Glew' the size of a walnut is enough for a pint of water. The second recipe, listing the various dishes and ways in which it can be used, could be translated without great difficulty into tips on use' to be printed on a modern stock cube or 'instant soup' packet. Portable soup in its original form survived, at least in recipe books, into the 19th century. How many travellers actually carried it around in their pockets or in little tin boxes, as recommended, is a question which seems unlikely ever to receive a satisfactory answer."
---Oxford Compantion to Food, Alan Davidson [Oxford University Press:Oxford] 1999 (p. 625)

"Pocket soup Also "cake soup." A soup that was boiled down into a jellylike mass that could be put in a pouch and later reconsituted with hot water. A recipe in the Lady's Companion of 1753 calls for boiling a leg of veal until the liquid in the pot thickens to a jellied stage when cooled. This is strained and poured into cups, which are then placed in a pan of boiling water until jellied. The gel is then cooled and turned onto a piece of 'new flannel', in order to absorb the moisture. The result was a very concentrated, strong jelly that was turned back into soup by the addition of hot water and salt."
---Encyclopedia of American Food and Drink, John Mariani [Lebhar-Friedman:New York] 1999(p. 246)

How did they make portable soup?

[1792]
"Portable Soup
Take three legs of veal and one of beef, with ten pounds of lean ham, all cut very small, put a quarter of a pound of butter at the bottom of a large pot or cauldron, and the meat and ham in, with four ounces of anchovies, two ounces of mace, a bunch of celery, six carrots washed well, a large bunch of sweet herbs, a sponnful of whole pepper, and a hard crust of a penny loaf; sweat it over a slow fire till you find all the juices are drawn out of the meat, then cover it with boling water, and skim it well; let it boil gently for four or five hours, then strain it off to settle, pour it into a pot, and boil it till it is a strong jelly, and as stiff as glue, season it with Cayan pepper and salt, then pour it into little tin moulds; let it stand till cold, then turn it out on plates, and dry it in the sun, or at a great distance before the fire, keep turning it oftn till it is quite dry; then put it in tin boxes, with a piece of writing paper between each cake; put them in a dry place for use. This is a very useful soup for travellers, or large families; for by putting one small cake into a pint of boiling water, and giving it a boil up, it will make a pint of good soup; or a little boiling water poured on a cake, will make a good gravy for a turkey or two fowls. It possesses one good quality, it never loses any of its virtue by keeping."
---The New Art of Cookery According to Present Practice, Richard Briggs [W. Spotswood, R. Campbell and B. Johnson:Philadephia] 1792 (p. 52-53)

Looking for more historic recipes? Michigan State University's Feeding America digitized cookbook collection offers serveral. Search recipe name: portable soup.

By the mid-nineteenth century, scientific advances (dehydration) and industrialization permitted the mass production of several foods based on pocket soup. Meat biscuits, dessicated vegetables were produced in factories and provided to Union Civil War soldiers. Knorr marketed dried soups to the general public in the 1870s. If you want to read more details on these later products, ask your librarian to help you find the book Pickled, Potted and Canned: How the Art and Science of Food Preserving Changed the World, Sue Shepard.