Hmmm…. I would think the number of stuffsacks carried would be more personal than "scientific," based on individual organizational wants/needs. For me, I carry many stuffsacks since, like most everyone here, I wear a pack with limited storage pockets; and I prefer to keep everything organized.
I also only carry a handful of items demanding waterproofness: insulated clothing, sleeping bag, and my camera.
1) My sleeping bag, insulated clothing, spare boxers, and spare socks are carried in an oversized drybag that fits snugly and horizontally at the bottom of my pack. Outdoor Research drybag.
2) My cookware, stove, and utensils are kept in a Spinnaker stuffsack fit to size. Granite Gear Spinnaker stuffsack.
3) My miscellaneous small items, morning/camp gels, firestarting, maps, navigation, emergency kit, spare batteries, etc, are kept in a small Spinnaker stuffsack. Granite Gear Spinnaker stuffsack.
4) My raingear is initially kept in a Spinnaker stuffsack fit-to-size, but, if not being worn, it is most often carried loose in my outer mesh pocket for drying — that's the Smokies for you. I primarily carry this stuffsack to be used as a pillow if the contents are dry. Granite Gear Spinnaker stuffsack.
5) My shelter is kept in the manufacturer's stuffsack, but will often be carried strapped to the outside of my pack for drying — re-arranged often to allow different surfaces to dry.
6) Food is carried in one, possibly two, Ziploc freezer bag(s) for high visibility and waterproofness. It should be noted that I often carry two spare freezer bags, one solely for freezer bag cooking, and one as a backup.
7) Small sandwich-size Ziploc for my camera — either carried in a hipbelt pocket or a pant pocket for easy access. When not in use, it is always secured in the Ziploc regardless of how dry the weather is.
8) Small sandwich-size Ziploc for water purification, sunscreen, bug repellent, lip balm, and other items I may need to use frequently — again, either carried in a hipbelt pocket or pant pocket. This is carried strictly for organization, but when I get lazy I will frequently carry them loose in the aforementioned pockets.
9) My packout bag is also a Ziploc freezer bag carried in my outer mesh pocket, and hung from a tree or bear hanging system as such (in my pack's mesh pocket). The idea is that rodents will go for the packout bag as a treat of least resistance in the mesh pocket, and not my food contents secured inside my pack. So far this has worked in the Smokies, for my packout bag has often been compromised by rodents, but my food and pack have not been. For a long-distance hike, I would probably elect to carry my food in something more odor-resistant if planning to hang it on the AT — my longest AT hike has only been ~50 miles.
For your question, I suppose only 4 of those would qualify as stuffsacks. For me, the only item carried loose is my foam sleeping pad; but I also elect not to use a pack liner or cover. However, I could easily see someone getting away with just carrying one, or none, stuffsacks if they elect to carry a pack liner and pack contents in a way that would seem blasphemously disorganized to me. My opinion is that the weight of stuffsacks and Ziplocs is so negligible that you should just carry as many as you feel comfortable with from an organization standpoint. HYOH!