I've been contemplating packs and dryness, and I'd very much like to hear what the wise and good folks here have to say.

I live in the PNW, and it seems to me that there are three categories of gear, and that packs don't really do a good job of handling them.

1) MUST be dry: sleeping bag, sleeping clothes, hammock
2) As dry as possible: warming clothes, food bags, stove, etc.
3) Definitely wet: Tarp, rain gear, clothes worn in rain...

I really don't want to put my wet tarp into the same pack bag with my sleeping bag. Has anyone here got a pack or a system that separates things by dryness/wetness category? Also, why have a "waterproof" pack bag if you're going to put wet stuff inside of it?