Honestly, buy a book bag...from Walmart. I use one (jansport, i think, recycled from my kids school stuff), striped down for day hiking, motorcycling, bicycling, etc. You can remove a lot of weight by cutting out dividers, and all the extra bling you won't use. The material is ballistic nylon and made for rough use. You can't make it as cheap as you can buy it. Since school is starting, you'll find them on sale all over the place. And...properly gutted, you can make a dandy day ruck sack from a book bag and might even get a couple nights out of it.