Waterproof Stuff Sack
Keep those sleeping bags dry. I have heard that sleeping in a wet sleeping bag is no fun. I don't want to jinx myself, but I can honestly say that after many hundreds of nights in the outdoors I can't remember ever having slept in a wet bag--even after being out in the worst weather you can imagine. I hope that doesn't change.
So often, I see bags tied to a backpack or dragged along loose in nothing but a garbage bag twist-tied shut. By the time it hits the tent, that garbage bag may be full of holes and rips, and the sleeping bag inside damp or soaked.
Here is a tried and true method for reaching camp with a comfortable bed to crawl into after a satisfying day in the great outdoors. Plastic bags are fine, but the trick is to protect the plastic. Your sleeping bag goes into one stuff sack, then into a good, heavy plastic bag (or two), closed on the end. That all goes into a second stuff sack. Then take care of it. Don’t let it lie in standing water, such as in the bottom of a canoe, boat, pick-up bed, or trailer.
It's especially important if you have a down-filled bag. Once down is wet, it's terribly hard to dry, and has virtually no insulating capabilities. Synthetic bags have come a long ways, but are still a little heavier and less compactable than down, but retain much of their insulating qualities when damp or wet. Find the best bags right here.
I have both, and take whichever fits my needs at the time. I have used this sleeping bag packing method for years on many dozens of trips in every imaginable kind of weather, and I can tell you it is worth the effort!