If you have an R.E.I. anywhere in your area it's worth a visit, they are very dog friendly and their dog products are of the highest quality. Last summer I took Mavis to the Santa Ana R.E.I. to get a dog-floatation device, and the guy working there had dog treats in his pocket, he became Mavis' best friend real quick.
When we go for day-hikes, I usually take 3 dogs, Dobie Mavis, Dobie/Boxer mix Katie, and Black Lab Toby. It would be alot of work for me to carry water and food for all 3 so they carry their own. Normal load for each dog is about a gallon of water, carried in 2 two-liter plastic soda bottles, one on each side of the pack. Six pouches each of "Purina Moist and Meaty" dog food, two folding nylon dog dishes(1 for food, 1 for water), dog treats, a cheap nylon-rubber doggie rain coat, and a set of 4 dog shoes. R.E.I. sells the best dog shoes, we use the ones made by Ruff-Wear. They also carry their own leashes, we always try to go places where we can get away with going leash-less.
If you get packs, start light with their loads; maybe only a quart of water on each side of the pack. Balancing the load evenly on each side is important, but it's also easy, especially if you're carrying water. Always carry dog-treats in the pack, and make sure your dog knows where the treats are. One or two trips packing is all it takes for your dog to be crazy about the idea.