I'm a walker and what you have listed is also my tool kit. My personal preference is to walk ALL client dogs with my leashes, for most I use a Mendota slip lead as they are easy on, easy off, and the dog cannot escape as that can happen with many ill-fitting client harnesses, collars, and leashes. And NEVER, NEVER walk a clients dog on a retractable leash, they are a major safety issue for you and the dog. My pockets are full of poop bags and of course, treats for the end of the walk.
And I never walk without a can of citronella spray in case a loose dog approaches and tries to attack, fortunately with over 3000 Rover walks I have never encountered an unfriendly dog.
In my car is a first aid kit as a just in case, along with spare leashes and other supplies. Frozen locks can be freed with a spray from windshield de-icer, and that has been needed recently. I also have a flashlight, a small tool kit with screwdrivers, adjustable wrenches and a hammer and I keep a few spare batteries for clients garage remotes.
At the meet and greet I always take the dog for a brief walk without the owner to see how they respond to me and how well they walk, for me that determines if I will accept the dog client.
Since I use the Rover App and report cards I ask the client for access to their WiFi network it makes it easier to send the card at the end of the walk, not one has ever said no.
Walking can be lots of fun but lonely at times with only the dogs to talk to so when I see others on the street I go out of my way to say hello and have a nice day, it has gotten me a few clients so be friendly.
Best of luck to you