I stock the same things I have on hand in our '72 hour kit' - food, water, bowls to eat/drink from, and some medical supplies (prepared for treating cuts and gashes mostly, but various websites can also tell you other handy stuff to pack or put into your emergency preps: 4x4s, tape, kerlix and poviodine). I wouldn't hike without this for my kids, neither for our dog. Don't forget a leash too.

One thing on backpacks - check with your vet and see if you dog is suited to wearing one, and an estimate of weight they might carry. There is alot of hip displaysia in dogs, and too much weight can also cause injuries (people too). We finally have a pooch without hip issues, so Sully comes along on hikes more often. I'd rather just carry the food and water myself, or sluff it off onto #1 son. Our dog loves to roam about when offleash.