I misread the title. Thinking "a pack of dogs"...
My Stitch carries a pack. I call it that, because I can't remember the English word, the Norwegian would be kløv.
First, your dog needs to be old enough to carry some kilos. And you have to start gradually. The smart thing to do is to get a pack, and just get the dog to carry it around, empty. In my experience, that is the most important thing. (I have to remember to tell you all on the forum about the lemons, great story)
After the dog decide that he (or she) can move with a pack on, gradually increase the weight. Remember to have the weight on the shoulder, not the back. Spending money on a good pack is actually not wasted money. I prefer the ones with sued leather on the inside. And remember to buy one that lets the elbows move freely, and also has rings and straps so you can tie the pack up so that nothing "swooshes" around. The pack needs to be firm.
I have never had my dog run with a pack on, and considering the weight in it, I would never make him run with it on. Around here the terrain is either pretty much straight up or straight down, so we don't run. Going downhill with a heavy pack on the dog is also an art, so remember that the pack you buy have a strap at the end of the "top" so that you can fasten a line there, to help your dog and prevent the pack from sliding forward.
Stitch can, when he is in OK shape, carry 15 kilo. Nia is too young (10 months) for a weighed backpack but I am going to buy one for her soon.
The only drawback about making your dog carry packs are show related.. the hairs in the ridge on the shoulders can get gnawed away..
Good luck.
Heidi