Please understand I am not trying to be a “know it all,” but the use of haversacks by civilians in the 18th century into the early 19th century was almost unknown outside of Militia Equipment, but not even then very often unless they were issued to the militia. (I am just as guilty as many other folks who used to use cloth haversacks in a civilian interpretation.) Civilians then used other things for that purpose and if a civilian got caught with a haversack on, he would have some hard explaining to do around military forces, because they would have believed he stole it or bought it illegally from one of the soldiers - as it was military property.
Civilians usually used a “Market Wallet” or a “Snapsack” to carry items sort of like folks use a “tote” or a backpack today.
A reproduction Market Wallet and info:
http://www.18cnewenglandlife.org/18cnel/wallets.htm#Market Wallet
A reproduction Snapsack is shown in the link below:
http://www.gggodwin.com/prod-916.htm.
Both Wallets and Snapsacks were almost always made from cloth and normally fustian was the common material.
.For leather in a Knapsack, we have to go with the British Military: However, goat skin was primarily used as a waterproof covering and much of the item was made from cloth:
French and Indian War: http://www.jarnaginco.com/FIcatframe.html
Rev War: http://www.33rdfoot.org/knapsacks.html
Hope this helps, Gus