I'll say "it depends" on your climate & on the pack you use. I've done the majority of my hiking in SE Alaska's temperate rainforest and a fair bit of hiking in Western WA where it rains about half as much. I chose a pack that's almost watertight, and I can get away with non-waterproof stuffsacks and no liner/pack cover even through all day rainfall.

I use a small stuffsack for my tent but no separate one my sleeping bag - the bag lives in the tent because it stays pretty dry in there, but the whole thing goes into a stuffsack because the outside of the tent generally gets too wet to go into my pack uncovered.

My clothes go into a compression sack because I have a small pack; the gear won't fit otherwise, especially if I'm carrying a two-person tent. I've been meaning to upgrade the compression sack to one of those rolltop "Event" ones; no side straps = less weight.

The only time I'll use something completely watertight is when I go paddling. Then, I'll use a roll-top pack liner and tie my pack onto the boat. The rest of the packing system stays the same.

Edit: Oh yeah, the bear bag thing. It's good practice to put the food into an "odor proof" bag, which is pretty watertight anyway. The hanging bag can be any ultralight stuffsack that's the right size.

Watertight stuffsacks are also good for general boating use. The don't have to go in a backpack.