Can't really give you much advise other than to post some more stamps. The airmail stamp is scott number c-47. The average retail sale price is .30 (cents each), that would be on the high side of the pricing. I see people try to get .99 or 1.00 on
ebay but that is way over priced.
Here is an example of an average retail price for this stamp.
http://www.ihobb.com/p/USAIRMAILSTA...SSMC047.htmlI'm not a foreign stamp collector so I can not say what you have off the top of my head.
Generally with very few exceptions unused stamps from 1940 to today are close to the denomination of the stamp. Feel free to use them as postage for the most part or save them.
Keep posting maybe you have some classics or something of value in other stamps.
My guess unless you know he
inherited an older collection from his father or you know he spent money for high value stamps the collection is probably like most and just a bunch of common stamps not worth much in value. Being that they are most packed together in glassine that would probably be a safe bet. But you never know.
It is still fun doing the hunt for what he has in his collection.