UPDATE 2019 - Still the winner, never had better SOS
WINNER - Best Biscuits and Gravy On a Road Trip!
4/11/2011 Atlanta; Marriott Chatham on Windward Parkway. 

Exit 11 on US 19 - 400 just north of Atlanta. We were there shooting During the Masters Golf  Tournament.  Best Biscuits and Gravy plus best Breakfast Buffet on our last three trips.  Great hotel, clean spotless, warm service personnel, alert management, nice fresh rooms, great Chefs, good food...

Package Buttermilk biscuits (Home made from scratch or store bought)
3/4 to a pound of sausage.   I used mild Italian, you can use Jimmy Dean, Bob Evans and others.  A good friend uses Deer meat ground (low cholesterol) exclusively and adds herbs for flavor. 
3 - 4 cups of milk
Flour or cornstarch as needed, usually four to six tablespoons. It's a small amount, doesn't matter as long as you don't let it burn on the bottom of the pan. 
Pinch cayenne, black, white or crushed red pepper to taste. (See options)


Biscuits - Prepare biscuits as instructed on package by the provider, slightly heavier biscuits are better to soak or absorb the flavors of the gravy.
Gravy -  I cut the sausage meat from the casings and browned the sausage in a hot skillet. I used a nonstick Calpathon saucier and a bamboo stirrer.  Also, stainless, as you get a good fond if preferred. 
After the sausage is evenly browned, return to medium heat. 
Add sifted flour a little at a time.  (I just run it through a small tea strainer) constantly stirring as making a roux or sauce.  When flour turns slightly brown, it means the flour is cooked and has incorporated. Keep adding flour to create the consistency you want. Slowly add milk and start stirring till the milk absorbs, constantly stir with whisk.  

You may add the following:
A can of cut mushrooms after browning the sausage.
You may further flavor the gravy, by adding dried sage or another treat is Garam Masala, and indian floral spice of great dimension.
You will see true Southerners drag out the Crystal hot sauce. 
Some will offer the biscuits with Cheddar and even Reggiano Parmesan Cheese over the biscuits while baking. 
Especially nice with the Italian Sausage. Sort of a unique Italian based combo.

Make sure that that nothing sticks to the bottom of the pan; as the flour browns it wants to stick to the bottom.  If the Roux gets dry, add a tbsp. vegetable oil. It needs to boil to thicken the flour. The heat is right to thicken the gravy; the longer you simmer, the more the reduction and thicker the gravy.  Too thick and you'll be using it as drywall patch.

The 1910 edition of the Manual for Army Cooks provides the basic recipe, for Shit on a Shingle or SOS, a quantity sufficient for 60 men to be served in the field, it is believed the beef was soaked to reduce the salt content: 

The Roux or creme sauce is the carrier for SOS, it is the crème sauce the corned beef, hamburger or pork resides in.  In France it could of been horse in the roux as horse meat is available in France.

Ingredients and recipe courtesy of an Army Chef.            
My friends Dad was in the army for 24 years and his mom used to make this for him. I love the stuff. The navy used canned chipped beef but I prefer the hamburger version.   Here is an official U.S. Army recipe for SOS: 

1/2 lb. ground beef 
1/4 tsp. salt 
1/4 tsp. pepper 
4 tbsp. sifted flour 
1 cup evaporated milk 
1 cup water 
2 tbsp. butter 

Brown ground beef in its own fat. Remove excess fat and save for making roux. Season with salt and pepper. 
To make roux, place 2 tbsp. reserved fat in double broiler or heavy pan. Slowly add sifted flour, stirring constantly over low heat until thoroughly blended. Cook for five minutes. Do not brown. 
Combine milk and water. 
Add butter and scald (not burn) in double broiler or heavy pan. 
Add roux to scalded milk, stirring constantly until thoroughly blended. 
Add meat mixture and cook about 10 minutes, or until desired consistency. Serve on toast.