The most desirable item is the Case, Small Arms Ammunition, 30-round Magazine. The case with magazine retention flaps was rejected during testing in 1971, but because of the immediate requirement in SEA this item was manufactured as limited standard. It was replaced with a similar magazine case in which the flaps were eliminated and other improvements made in 1972. So this example was limited procurement and should bring a premium price.
The canteen should have a year of manufacture molded into the bottom. The Cap, NBC, M-1 was adopted in 1981. The canteen was inexpensively manufactured in large quantities, was considered expendable, and is very common.
The Canteen Cover, Water, LC-2 was adopted in 1975. If the contract information on the back is legible (DSA or DLA-100-C-(two numbers)-(four numbers) the two numbers represent the fiscal year the contract was negotiated and is roughly the year of manufacture. If the contract was awarded early in the fiscal year the item may well have been manufactured in the current calendar year. For example a fiscal year1988 (July 1, 1987-June 30, 1988) contract the item may have been manufactured during the last six months of 1987 or later. Sometimes contractors were awarded additional work and the contract continued for a few years past the fiscal year. In any case a very common item and more useful to hikers than collectors.
The Belt, Individual Equipment LC-1 was adopted in 1975 and replaced with Belt, Individual Equipment LC-2 (plastic buckle) in 1982.
I am not a collector so cannot estimate current market value. As previously mentioned the ammunition case is a very desirable item, and should bring a good price properly identified.
Suggest "American Web Equipment 1967-1991" by Monroe and Pickrall for history and identification of U.S. individual field equipment of the era.