There is a significant difference between "waterproof", "weather resistant", and so called "all weather" bags.

Waterproof bags can be tossed into the water; your stuff will stay dry and not get wet. Typically, these are rubberized roll-up sealed bags, no zippers. Brands like Aquapac and Tyr. I use this type to carry camera gear on the water (rafting, canoeing, kayaking). I use a separate padded storage bag (I like the Lowepro Omni line, since discontinued). The advantage to the Omni's is that you can also put them in Pelican waterproof hard shell cases.

Weather resistant bags will have waterproof material and sealed zippers. They can take direct exposure to water as rain but I wouldn't submerge them or splash them repeatedly (but they might help your gear survive in case of an accidental dunking).

All-weather bags will have water resistant material and come with a rain cover for extreme conditions.

Personally, I only trust waterproof bags if I'm on the water.