How do I cook chicken and asparagus over an open fire?

You have two delicious choices. Both require a bed of coals, so I'll start with that.

You'll need to build a fire with the logs stacked 'log cabin' style, and let the fire burn down to coals. You want a deep red coal, just starting to darken on top. The coals should look something like this.

You can bake, or bbq the chicken and asparagus. Both are delicious methods.

To bake, wrap the chicken, asparagus and a starch like potato gratin style in layers of tinfoil. Use the starch around the outside, you'll sacrifice a layer of it as some of it sticks/burns to the tinfoil. Put the most delicate item in the middle, in this case the asparagus, and the chicken around the asparagus. Add a generous amount of butter, salt and pepper and bake for about an hour buried in the coals. Corn or green beans are also very good, and can be sacrificed a little around the outside to preserve your meat and vegetables.

I would layer it this way.

 1.Coals
 2. Tinfoil
     2. Potatoes 
     2. Generous dollop of butter
     3. Salt & Pepper 
     4. Green Beans 
     5. Asparagus
     6. Chicken 
     7. Potatoes
 3. Tinfoil
 4. Coals

Now, BBQ. You'll do it very much like a charcoal BBQ. Keep the grate close to the coals, you can generally test the heat by holding your hand above the grate, you should only be able to keep your hand there for a second or two at most.

Grill the chicken like you would on a bbq, and roast the asparagus on a cooler part of the grill. I'd marinate both before putting them on the grill. I'd also try to get an aromatic wood like hickory or mesquite, pine will impart a resinous taste.

The most important thing is to cook over open coals not over open flame. You'll get more even heat and no sooty smoke. Just build up a fire with some good-size pieces of wood and let it burn down so the flames are gone and you're left with a nice set of red-hot coals. Then start cooking.

At this point, theoretically, it's just like cooking over charcoal briquets, although you'll probably have less control over the distance from the food to the coals. The grate might also not be as clean as you'd like.

If you want to cook directly on the grate, I think grilled asparagus is absolutely amazing. Just olive oil, salt, and pepper and then cook over pretty high heat until it wilts and blackens slightly. You'll want to have tongs. Grill the chicken like you would in your backyard.

An alternative for the true boy scout camping experience would be to do a tin foil dinner, where you wrap the food completely in aluminum foil and then bury it in the coals. Google gives lots of hits for this technique, although people usually use ground beef and not chicken.

Wrap the chicken and veggies in the tinfoil but don't cook for an hour- probably a maximum of 20 minutes