|A four pocket 5.56mm bandolier and safety pinned charger|
A bandolier packages what would otherwise be loose ammunition into a mobile package, allowing a fighter to replenish emptied magazines quickly. Unlike loaded magazines, bandoliers work well for deep storage--there are no springs to worry about. They're also fairly inexpensive, though the price has gone up in recent years; current "repack kit" prices run around $6 to $10, depending on the source.
M16 bandoliers come in different flavors--four pocket and seven pocket, with the seven pocket being the older design, intended for 20 round magazines. The British have 5 pocket bandoliers, sometimes also available on the surplus market.
The fabric bandolier itself is made of fairly low quality materials, and old, surplus bandoliers typically show quite a bit of wear. They're not pretty, but they work. Inspect your bandoliers to any major tears or other flaws before using them.
The four pocket bandolier has a white string running through the bottom half of each pocket. This string that can be removed with a tug, expanding each pocket to 30 round magazines size. This is a very useful feature if you were to find yourself separated from other fighting gear, and other reason why bandoliers are a good thing. If you're putting back an ammo can or two of loaded bandoliers, storing four empty magazines with 'em would be a good idea. Unfortunate, this white string is also the source of one of the most common flaws that I have found on old bandoliers. It will commonly give way on one or two of the pockets. Luckily, this simply expands the size of the pocket and doesn't cause major problems with functionality.
Stripper clips are fairly easy to find at gun shows and on the 'net; if you're lazy, Federal even sells ammunition already loaded into stripper clips. They are generally reusable--just make sure not to put too aggressive of a fold into the brass retaining tab at either end, as this will be the point of wear and failure for the clip. Another tip--don't use steel cased ammunition in these--it will hang up and not charge properly. Good brass ammunition will slide off cleanly.
Cardboards can be a bit harder to come by unless you're buying a repack kit--and then, many people balk at paying for flimsy cardboard that you have to glue/tape together. I've heard of people cutting/gluing their own to save on cash. Might be an option.
The charger is a key piece and what lets you load the ammunition from the stripper clips into your mags--so don't lose it! Good magazines will have a little groove at the rear of the mag, which is intended for the wide end of the charger. You then insert the stripper clip into charger and press down firmly on the cartridges, pushing them into the magazine.
Loading magazines with a stripper clip and charger takes a little bit of practice, but once you've got it down, your loading times will decrease dramatically. You don't need to be the Flash to go from empty to fully loaded in around 10 seconds. That's big.
If you're looking for bandolier repack kits, your best bet is a search of eBay, Gunbroker and similar sites. I would be hesitant to pay more than $7-$8 for a kit.
One question to any active duty readers--can you confirm how U.S. forces are currently issuing ammo? Are the venerable bandoliers still in use?