I sure respect any dog owner's decision regarding her four-legged helper. I'm blessed with a very strong Malmut-Chow mix, now six years old, with plenty of trail experience. We did 200 continuous miles on the CT last year and will complete the 300 east of that this year. Not to mention numerous miles on the GET in NM. Buddy weighs in around 90+ and is strong as a small horse. Still I was concerned how he'd hold up to the daily grind on the CT. We hiked the western segments through the San Juans, so lots of ups and downs. He did great.
Buddy got a new pack for the adventure. A Wolfpack Bonzai, and we both really thought it an improvement over his old REI pack. Rides well, only one strap under the dog near his belly.
Check their wares out.
Some dog breeds (like Buddy's) have a long history of packing. Native Americans in the southwest (and elsewhere) harnessed dogs with travois or packs, depending on the terrain. My point is, while not appropriate for all dogs, some breeds, some dogs, really love to carry a pack. I know mine does.
Now, my little 14-year-old terrier mix, that's a dog of another color, so to speak. Buddy carries her sweater and sleeping pad. And she only does overnighters now.
So, to answer your question, maximum weight for Buddy is 15-20 lbs at beginning of a 5-day stretch. He requires no sleeping gear, but he carries all his food, a drinking dish, two 2-Lt Platy's just in case of a dry stretch, a leash, and my rain gear. Having rain gear in there puffs out the pack and allows quick access. Oh, and he does carry trail garbage we create or find. He's an all around super trail friend. Once or twice, in very dry stretches, Buddy has carried more weight, but prefer not to do so. Those 2-lt Platy's are not filled unless absolutely necessary. He doesn't seem to mind carrying them, though, if he has to do so.
I know we love to pamper our dogs. It's a means of showing our love. But dogs are by nature tough animals. Love them and work them, that's my philosophy. But as in all things trail, HYOH!