I've been trying to decide on a pack so my dog can carry some of her gear. What features do you look for and do you have any to recommend?
Edit: My dog is about 38 lbs. (and super cute)
Love this question, I could talk dog packs all day! We've probably owned four or five different styles between three dogs, and honestly liked every one of them, because fit is the most important factor. If your pup is like mine, they love to lay down in puddles! Sadly, wet straps make for rubbing and potential chaffing if the fit is no good, which do not make for a pleasant hike for your doggo. We have a great overview article about Hiking or Backpacking with Your Dog in our REI Co-op Expert Advice, which talks about fit and that is really what makes a great dog pack.
Otherwise, I always look first at capacity (usually measured in liters in the specs). A lot of our dogs' backpacking gear is big and fluffy (think bed and jacket) and it is always nice to not feel like you're zipping an overstuffed suitcase! For the same reason, external attachment points or daisy chains, make it easy to clip on wet dog bowls to dry as you hike or even a second sleeping pad for winter backpacking. There are lots of other features out there, but I would give up any to make my puppy comfy in a well-fitting pack. Hope to see you and your pup out on the trails!
I love the part in the linked article: "A maximum of 25 percent of body weight is a rough guideline." Sometimes we try to load too much on our critters. 25% of 38lbs is 9.5. That can be hit fairly quickly. Also think about the environment that we taking our dogs with their packs on. Hot, humid locations will trap body heat in and possibly overheat a dog. Rest time without the pack in place is important to think of.
A saving piece of any pup-pack we've had is a handle on the pack. REI used to make a great pup-pack but sadly discountinued, however the handle saved me (and my dog) several times on the trails.
Using a handle we could help him on ladders, steep descents and even tricky water crossings. I think a lot of pup-packs still have it and i would never choose one without it.
Love that you mentioned the handle. We use the Mountainsmith K9 pack for our dog and the handle is super useful to help give her an edge when climbing rock faces. Just this weekend we headed up metal rungs, but there was enough for her to climb on but the handle helped us make sure she didn't backslide.
I also use the medium Mountain Smith K-9 for my 60 lb Malinois. She prefers this pack to a regular harness, and the handle is great for creek crossings. It has a couple of nice spots for a bowl outside, and the pockets are very water resistant. I sprayed it with nik-wax for keeping out water and pack food and snacks in ziplocks. This pack will hold fives days food, snacks, small blanket, and a tennis ball. Once adjusted it,s easy on and off for breaks.
The number one thing I look for is a good fit. I like packs with straps that go across the chest in a Y shape and also have a belly band. Every other pack feature is secondary to fit. I brought my dog to REI to try on packs in order to find 'the one.'. My pup couldn't go in the store, but an employee escorted me outside with some packs to try on.
I 100% agree with @TravelKate . The handle on top is critical. I have had to use the handle countless times to assist my 100lb dog in getting over slippery terrain/rocks/onto platforms, etc.
I'm sure some other packs have something similar, but i'm obsessed with the ruffwear palisades saddlebag attachment. You can take the saddlebags off without having to remove the entire pack. It is extremely helpful after a long day of hiking, or even just taking a break, to be able to remove the weight from your pup without having to take the whole pack off. It also makes it easier to put the pack on in the morning. You can slip on the harness, then attach the pack. Then you aren't wrestling the full floppy bags over your pup's head.
Other big thing to look for is durability. My dog frequently forgets how much wider he is with his pack on and tries to slip through spaces he is too wide for, or walks too closely to rocks/trees. His ruffwear pack is 7 years old and has been used on approximately 900miles of backpacking trips and you can't tell. The one thing that has broken on the pack is a buckle. I sent an email to ruffwear and they had 2 new buckles in the mail for me that day.