I love to tool around town with my 2 big dogs in the car. They go from the house, into the garage and straight into shotgun spot ready to ride. No leashes. It occurred to me one day that should I have car trouble and need to be towed, or God forbid an have an accident, I need to be able to corral and control the dogs. That was the start of my doggy bag. Obviously, if out and about on a leash you need your poop patrol supplies so add my bag dispenser and I have a hand sanitizer clipped on there as well.
Having family out-of-state also means overnight travel with the dogs. Add food, treats, meds etc. Then I went nuts! My bag has a water and food bowl. The food "bowl" is a disposable plastic sealed bin filled with dog food. I have re-purposed bottles, filled one with food, the other with water and all are decorated in doggy theme because I don't have enough to do and love wasting my time and scrap-booking supplies/tools!
On the road with the dogs, I quickly realized we need toys as well as grooming stuff. So toss in a tennis ball, squeaky toy. Add the brush (poodle ears do need combing) and some wonderful wipes in case the dogs decide to go roll in something that smells dead - as they love to do.
Because I have a stubborn barker - I have a muzzle and Halti just in case. For my - "I refuse to walk nice on a leash bitch" there's a choke chain collar. You have to tailor this kit to your lifestyle, your dog's personality and their needs but I love knowing that I have this with me to make life on the go with my furry friends more pleasant and comfortable for us all.