I am unaware of any peer reviewed, double blind study not financed by the bouillon cube cartel that has assessed the efficacy of cubes in a survival context, so the jury is still out, or, rather, hasn't yet been selected...

While food in of relatively less priority in most short time survival contexts, dehydration and electrolyte balance is critical, as is morale. I usually have room in a carefully packed kit to insert packets of tea, coffee (Via is preferred), sugar, or what have you. Bouillon cubes are just fine, provided you have water, but they aren't critical.