This is an easy way to make a recon wrap used in the military. Can be worn in many different configurations. They sell for roughly 20 dollars but why buy what you can easily make.

Step 1: Materials List

gonna need an old t-shirt, any color and the longer the better. (make sure it's a "breathable" material)
Sewing machine
scissors

Step 2: Measure and Sew

Make sure the t-shirt is inside out. You want to make a tube a couple of inches bigger than the diameter of your head so it won't cut off your circulation. So do the measurements and mark accordingly. Pin the t-shirt at the bottom so it won't come apart and begin sewing along your lines. Doesn't have to be perfect, it's just a sweat rag.

Step 3: Cut the Excess

cut off the outside portions (sleeves) leaving your seam intact. Also cut the neck area of the t-shirt as shown, roll it down to create an even edge and tack it in place. T-shirt should still be inside out.

Step 4: Sew Along Edge Creating a Seam

sew around the neck line fold you created. Careful, don't sew both sides together, your essentially making a tube. When your done cut the excess of the inside edge.

Step 5: Now Go Into the Desert My Friend

Many different ways to wear these depending on the situation. My favorite is the headwrap configuration for wicking the sweat away. Keep a few in your camping and ditty bags. They can be used as an emergency sling also.