The daypack designs are essentially about either school book and laptop bags, or travel backpacks. Almost all are now hydration compatible, so you can transfer over your bladder and drink tube. What destroys most daypacks is carrying way too much weight, in which case, a decent and comfortable strap with hip belt is ideal. Vented back panels weigh a bit more, but they can be worth it, especially in a tropical climate or during aerobic exertion. Flat black or crazy printed, Valhalla Pure Outfitters has a huge selection to choose from.