Almost everything tastes better in the outdoors. Even bullion cubes approach tolerability. However, as soups and sauces are the basis for much of my one burner cuisine, I've looked for means other than bullion cubes for creating rich, flavorful backcountry soups and sauces.
The best alternatives I've found are glaces and demi-glazes, real soup stocks reduced to a gel like consistency that are highly concentrated in flavor, low in salt, and require no refridgeration for reasonable periods in warm weather.
I used to make them myself, slowly reducing clear stocks for many hours. Now, there are a few commercially available glaces. The one I've used is by "More than Gourmet" called a "Demi-Glace".
Flavors range from veggie to chicken to beef to seafood and beyond. Individual packets of 1.5oz and 16oz bulk size are available. The small pack is under $6 dollars and makes from 1 to 3 servings depending upon strength. Far superior to the flavor of bullion, just add water for a real gourmet treat.
Glaces are now a staple of my backcountry kitchen. Though I haven't done much boil-n-bag cooking glaces should provide a rich flavor boost to the technique.