I didn't read all of the advice that you received (or clarification posts you made), but I have to assume that you probably have a synthetic sleeping bag and it is taking up the majority of the space (if I'm wrong ignore my post). Fork over a few bucks and buy a good down sleeping bag. If you still don't have room in your pack for food then throw out the kitchen sink...
I would agree with all those that told you to leave the puppy home. If you are willing to quit before leaving your driveway, you don't need the added headache of taking care of a dog along the way.