If you are on a budget, take a look at this Rag & Bone Backpack. It's a popular piece for a good price. Another savvy option is this Cabas Rucksack. While the price is competitive, be sure that this product will become a great addition to your wardrobe. You might also want to consider this Raf Simons Backpack. The price is very reasonable, but the effect on your wardrobe will be pretty fantastic.
If you're in a Treat Yo' Self mood, then what you're looking for is this Rucksack. It's more expensive but worth your money. While you're at it, also have a look at this Pierre Hardy Backpack. Yes, this item is expensive, but it does not mean it's not worth it. And one more item you might be interested in is this Givenchy Backpack. 'Cause you deserve nothing but all the finer things!