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I use this:
Amazon.com: AmazonBasics Backpack for SLR Cameras and Accessories (Black): Camera & Photo
Quality and size is quite decent considering it's price. There are a few people complaining about the top handle breaking but so far mine hasn't and I've had it for at least two years now. I use it most during hikes with my wife along with our 3 and 6-yr old. If you're only taking one SLR body and two lenses plus basic accessories (Flash, charger and spare battery), you should be able to fit a few "
Clean and Dry" stuff in the same compartment as your gear....baby clothes and diapers mainly.