The US Army modular sleeping bag complex is a very good system for the buck. Here's the whole package: the Intermediate Bag, Patrol Bag, Gore-Tex Bivy Cover, and the compression sack.

Meant to be usable in any environment or weather, the US Army modular sleeping bag system has it all. The innermost bag is the black Intermediate bag, and it is buttoned inside the outer green Patrol bag. If waterproofing or additional protection is required, a Gore-Tex bivy cover will snap on top of the whole thing. The modularity has the added benefit of "capturing" insulating layers of air between the bags. The combined weight of the bags, bivvy, and compression sack is 3.9 kg / 8.5 lbs.

The Patrol Bag

The green Patrol bag is a good choice for summer use and does not take much space either. The outer material is 70 Denier nylon fabric, and the stuffing is Polargard® HV polyester, which does not absorb too much moisture and dries pretty quickly if it gets wet. It closes with a heavy-duty zipper and has a large hood. The zipper can be opened from both ends, so if required, the feet can have some air too in warm weather. The zipper is accompanied by snap fasteners, to which the other components can be attached.

• Official Extreme temperature rating about 10 degrees Celsius
• Weight about 1000 g / 353 oz.
• Length about 229 cm / 90"

The Intermediate Bag

The Intermediate bag is quite similar, but black, thicker, and has a double insulating in the feet. It also features a slight tightening around the chest area to prevent cold air from entering the bag from the hood opening.

• Official Extreme temperature rating about -10 degrees Celsius
• Weight about 1900 g / 670 oz.
• Length about 216 cm / 85"

The Bivy Cover

For wet weather the bivy cover can be used. Although meant for this system, it can still be used with most other sleeping bags, as it is quite large. It offers good waterproofing capabilities and a bit of extra insulation while still letting moisture out.

Care

Don't wash sleeping bags unless you really have to - if you do, wash in 40 degrees Celsius (104 F). Usually washing can be rendered virtually unnecessary by using a liner bag to collect any grime. Then just wash the liner. If you wash the sleeping bag or it gets wet, open the zipper and hang dry.

Genuine army surplus

Used, but in good serviceable condition. No bananas inside. However these are used, so the insulation properties might not be as good as new. This is an affordable choice for a year-round sleeping system, suitable almost every temperature and weather imaginable, and probably beats every civilian bag in durability.