Assuming your dog is fully developed, they can carry up to 1/3rd of their body weight and be totally fine (closer to 1/4th if they are a breed prone to Hip Dysplasia).. My dogs (two Hungarian Vizslas) are 3 yrs and 2 yrs old. They each have their own Ruff Wear Approach Packs. They share an REI adventure Dog tent. They carry their packs, their tent, food, collapsable dog bowl, tether, and a nighttime treat. They each have their own foam pad they carry as well. Fully loaded up, their packs weigh about 6 pounds each (well under 1/4 of their weight). Each dog weighs in at about 40 pounds. Something we have used in the past is a 20x30 bathroom rug as a pad for them. Folded up tight it fits in their pack and isnt all that heavy. They have never had to carry more than 8 pounds, and even at 8 pounds they are still under 1/4th of their weight. With 6 pounds loaded up they could hike all day if I let them. They love every minute of it.
Important things to do before hiking with dogs is:
1. Obedience training. Not where they come 75% of the time when called, it must be 100%.
2. Keep them on lead, even tethered in camp. Your dog may come 100% of the time in the back yard but what would he do if he saw a rabbit/squirrel/fox?
3. If keeping them in your tent, train them to go to an area of the tent and stay there until you release them. You will never get one wink of sleep in a tent with an untrained dog. They will move all over the place.
4. Bring something for them to sleep on. Someone already mentioned the walmart pad which is great. They will be very restless not having a pad.
5. Make sure they know not to bark at strange noises, animals etc.
6. Keep their load under 1/3rd (1/4th if prone to hip Dysplasia).
7. ENJOY IT! there is no better hiking partner. Just like hunting, hiking with a trained dog is very much fun.