I’ve become a fan of compression dry sacks as they help to significantly cut down on volume. I use at least 3 of these in my journeys. One for the sleeping bag, one for all my clothing, and one for the tent fabric. I note that you don't want to get anything bigger than a 15 liter because if your bag is not very full, it gets difficult to compress it, and if you are filling a big 20 or 30L bag to capacity, the compressed pack will still be really big. You only need a 30L bag if you have a really really big tent, like a 10 person tent.
The Youtube video below from East Coast Kayak does a very good job showing how to use the dry sack and pack your gear. They show a rip in the bag, which I have never had it happen to me, so I think it must not be very uncommon.