We know baskets were being produced before the fist beer was made. They were fitted to backs through out history. It looks like, based on paintings and drawings, that our 'pack baskets' are more of an 1890s thing. Could some one have been using them before? No doubt. However you could go with some sort of knapsack for a more common article.
I have not used one a field for about three years although they are used for storage at home and could be packed if needed. Townsend makes some nice looking ones that are better shapped then the common cube style,but are a might pricy.