I have a backpack for my dog, and I've used it a lot. I put a baggie right full of rice or navy beans in each of the 'saddlebags' on either side. He is about 30 pounds so I think too much more might cause problems. I like it for the bit of extra work it gives him, so he tires out a bit more. I don't use it in the summer though as I think it would overheat him being made of polyester and not breathable. Unfortunately, I can confirm that it did not help with pulling on the leash.

I went to a dog trainer for that, and she showed me how to give a correction, and that was that. Pulling and ignoring the holder of the leash is definitely a respect thing, that is the way to end bad leash manners. And I can tell you my dog had unimaginably poor leash manners at 1 year old!