Is your sleeping bag synthetic or down?

If synthetic, you about have to compress it or get a ginormous pack, because synthetic insulation is so bulky. However, don't compress it any more than you absolutely have to. One of the reasons synthetic bags have a significantly shorter life than down bags is because of the need to compress it so much to get it into the pack. Unless the bag is extremely bulky, shoving it into a stuff sack or dry sack the size of the one that came with the bag should be enough.

If down, a compression sack is not a good idea as excess compression will significantly reduce the life of your (presumably expensive) sleeping bag. Use an ordinary stuff sack (assuming you have a waterproof pack liner) or a plastic bag or a dry bag. Some just put it loose at the bottom of your pack (again, assuming you use a waterproof pack liner to keep it dry). Any of these will compress it enough to fit in your pack. Many good down bags will compress down to the size of a baseball, but IMHO that's not a great idea.

In either case, for longer bag life be sure to get the bag out of its compressed situation as soon as possible after your trip!