Blanket & Poncho
The soldier's blanket roll is his bed, extra warmth for his upper torso when he's on the march, and a place to carry all sorts of extra things that won't fit in his haversack. On the outside of the roll is either a gum blanket or a poncho. Both are sheets of rubber backed with fabric and fitted with grommets so that they can be used as a simple shelter if a tent isn't available. Ponchos also have a slit in the middle so they can be pulled over the head to form a "rain coat." You'll probably want a poncho since it can double nicely as a gum blanket. Inside the roll is either a wool blanket or a quilt. These vary in size and thickness, but if you are sleeping "campaign style" your blanket is all you've got to keep you warm at night so you may want to purchase a good one.
When campaigning, soldiers frequently doubled up with a "pard", sharing a pair of bed rolls. They would put down one gum blanket, lie on top of it, side by side, add both blankets, and then the other gum blanket on top. Then they "spooned", cuddling up to one another (in a manly way, of course) to stay warm. This arrangement worked well even in the dead of winter.
If they didn't have a backpack, soliders would roll up their mess gear and other loose items in their blanket roll, giving it a final twist before tying it with a rawhide cord and slinging it over their shoulder.
If you want to save some money, simple gray wool blankets that pass well for period ones can be had at many army surplus stores for about $20.
C & D Jarnigan & Co. (2000 prices)
#320 Poncho $47.50 #6003 M1851 US Army Blanket (plain gray)
(1998 price - not in 2000 catalog)
For really authentic blankets, check out C. J. Daley: www.cjdaley.com