Try to get something ordinary looking – not the military I’m-ready-for-anything and my-bag-is-valuable look.
When a crisis happens, there will be a lot of people looking to steal from others who have the supplies they want. Don’t encourage them to target you – by having a valuable-looking bag.
Yet your bag should be quality. Some people say 1000 denier nylon is the way to go. I say this is too heavy and you can get by with 600D just fine.
Double or triple stitching in the important areas, like shoulder straps are helpful, though. So are YKK zippers – they last virtually forever.
Should you get a two-strap backpack or a one-strap sling bag? Each have pros and cons. The one-strap is great for the everyday ride on public transportation. Easily shift the bag to carry in front of you and avoid those pickpockets. But your back and shoulders will get super tired of carrying one of these for any distance.
Two straps with extra sternum and waist straps are the way to go for the distance.