I dont know if it would be big enough for what you'd need to carry, but I've been using one of Duluth Packs double shell bags for quite a few years now. They're made to carry shotgun shells, but I've never use it for that. They're made out of canvas, with an adjustable leather shoulder strap. It has one main compartment, with two outside pockets on the front. The cover has two leather straps with roller buckles to keep it shut. I got mine in olive drab, but they come in different colors. I was surprised at how much they actually hold for their size. I carry an extra pair of gloves in a ziplock bag, something to eat and drink, a whetstone, hand warmers, compass, a small flashlight, an extra string, toilet paper, and more in mine. It's so handy, I'd hate to be without it. They're very well made too.
They make actual haversacks too, now that I think about it, but i went with the shell bag, because It's a little smaller, and holds what I need it to.
Bob