I agree with what Omaha said, make sure to get your dog used to it first by wearing it empty for a bit. In fact the bag I have breaks down into two pieces, 1 is the actual bags and the other is kinda like a saddle. Maybe just have Diesel wear the saddle part around first. Ginger doesn't mind wearing hers one bit, as you can see in the pic. She's carried all kinds of things, mostly just her stuff, like food, water, toys, doo doo bags, and whatnot. I have had her carry stuff for us too but nothing too heavy, like keys, wallet, cell phones, water bottles, stuff like that when we hike. I had her carry a couple beers for me one time when we walked down to the river, it sounded like a great idea. However I didn't account for her shaking them around on the walk.
Yeah lmcjaho you could probably fit a couple bottles of soda in it. Are you thinking 2 litters? That might be a little too heavy though, guess it would depend on how far you're walking too. Also I always try to balance Ginger out. You can probably find the saddle bags at most pet stores. I got Gingers at either Pet Smart or Pet-Co.