Just a note--a stuff sack with drawstring closure is not waterproof--water can enter the closure. I'm not the only backpacker around who has slipped and fallen while crossing a difficult stream ford. A dry sack is waterproof. So is plastic if properly fastened. Some folks line their pack with a 2-mil plastic trash compactor bag (make sure it isn't perfumed!) and don't bother with a sleeping bag stuff sack at all--just put the bag in the bottom and put everything else on top. Others use a mylar turkey roasting bag. If you have a synthetic bag you almost have to have a compressor stuff sack to make it fit in the pack. You don't want to use these for down bags, though (they do plenty of damage to synthetic insulation, too). I prefer to use a Sea to Summit Ultra-Sil dry bag for my sleeping bag and another for my insulating clothing. These weigh little more than a standard stuff sack. They also have a version with an eVent bottom so you can squeeze out extra air. I do use a lightweight stuff sack for my cooking pot (to keep the lid on and therefore keep the stuff inside it, especially my stove, from falling out) and another to organize my toilet articles and first aid. Plastic bags can work just as well, though. Stuff sacks add to pack weight, so don't take any more than are absolutely necessary. And get light-weight ones, like silnylon.

You don't need a stuff sack for your tent, either--depends on how you want to pack it. Just make sure you won't lose any poles or stakes.

Depending on where you camp, you may want to hang your food in a stuff sack or you may be required to use a bear canister. I personally use an Ursack where a canister is not required, because throwing things (something I can't do with any accuracy anyway) exacerbates arthritis in my shoulders. If you hang your food, I'd get an OP sack big enough for the food to put inside a lightweight stuff sack. The OP sack takes care of the waterproofing and blocks most odors, making your food sack less attractive to small critters and birds who are not deterred by hanging food sacks.