Do we keep them and toss them away later? Or do we toss them at the client's home?
I am a daily walker with a heavy workload, I never use a client provided leash as I prefer to use my own. I use slip-leads and Walk-EZ leash/harness for pullers. I provide my own poop bags and I am fortunate many of my area's have poop stations or I use the clients trash can.
When providing services at the client's home, it's preferred if they provide the collar with tags, harness, and leash. However, I try to bring additional ones and keep with me in case I can't locate theirs or it's non-usable (unsafe condition or retractable). With poop bags, I try to find a non-private community garbage pail during walks. I'd suggest discussing both of these questions during the meet& greet, so everyone's understanding matches.
Yes, those retractable ones are the worst!
I discuss this at the M&G to determine what the client wants me to do. Normally for drop in visits (I don't do walks) I put the bag in the client outside trash container. For long-term visits (2+ days) I will bring or have the client provide a large trash bag. I leave that outside out of reach of the dog(s) and put the individual poop bags in it. The last visit I then put that into the client's outside trash container.
I had one client that had a diaper genie type container in her garage that she wanted me to use for the poop bags.
I would also suggest that if you are doing long-term drop-ins while the owners are away, discussing how to handle the outdoor cans. They may have a housekeeper or neighbor putting them out at the curb/alley, but if they're not, they might be willing to pay you to put them out/bring them back in.