Indeed. Like people, dogs need gradual conditioning, especially for enduring long-distance weight-bearing.

Gidget has done a lot of pack hiking, walks at least a few miles a day, every day, on sidewalks so her paw pads are toughened and she does a lot of bikejoring (6-10 miles at a time) so she probably starts out ahead of other dogs. But she's six years old, has thick fur (blessing in winter, problem in summer -- especially on pavement) and veterinary care would likely not be accessible on such a trek.

I would take extra care with her on such a journey. No pack. That's why I have a bike trailer for dogs -- so she can walk as much as she can and she can ride when tired or injured.

Something I should do is get her comfortable with wearing booties. I have a couple sets for her to avoid ice buildup in her paws when it snows. But she does not like them, at all, and acts hobbled when forced to wear them. Booties could be a lifesaver for a dog doing miles a day on pavement.

Anyone who wants to seriously prepare for bugging out should have a bike and bike trailer. Even if you start out evacuating in a vehicle -- that bike and trailer could be priceless backup. There are bike racks for every kind of vehicle and bike trailers fold down, come apart and can be used for storage in the vehicle.

I use the bike dog trailer at campgrounds for hauling firewood and bags of ice. It's rated to carry 100 pounds (Croozer dog trailer). You'll note at their website that they also carry dedicated cargo trailers.

http://www.croozerdesigns.com/

Also have a Burley "Nomad" cargo trailer with cargo rack:

http://www.burley.com/

This is a great thread, harkening back to others' observations on ETS that a survival basic is being in good physical condition at the outset of a crisis.