As part of your pet sitting business you will need a systemized way to manage your customers keys. You will be in possesion of clients keys during the duration of their visits and some customers may also prefer you to keep a key permanently on file for them so it is immediately available in an emergency, and convenient for them to schedule future pet sitting services.
Some clients may wish to give you a garage door opener or code instead of keys. These work great for easy home access but you will be in trouble if there is a power outage as often garage doors will not open. For this reason I would recommend that you always get at least one copy of their key as a backup.
You will need to make sure that after the client gives you their key at the initial interview that you have:
1) a secure place to store it until their visits commence
2) a safe place to transport it while you are completing their visits
3) and a secure place for permanent key filing.
I recommend that for security reasons that you never label customer keys with either their name or address. If a key is lost you don’t want someone who finds it to be able to look up the address of your clients. I label my client keys with a number only and then use a cross referencing system to match clients identity to the key number.
For temporary and permanent storage of client keys 
I use a lockable key cabinet manufactured by MMF in the picture on the left. It comes with everything needed to label and store keys and gives me a two key system so that I can keep a master key on file and give the other key to my pet sitter to carry to visits.
I always request that clients give me two copies of their keys at the intial interview. Having a master means that if for any reason a sitter cannot make it to a visit that I can fill in for them at last minute notice, and it also means that I always have a spare key if the sitter misplaces their key.
This system comes with a red permanent tag for the master key and a white tag with same number for the sitter key. It also comes with the blue cross reference book for matching customer identity to their key number. Of course it is good practice to keep this book separately from the key cabinet.
These cabinets come in different key capacities and can be attached to a wall in your home and kept locked. You can purchase them online at office supply stores such as Office Depot and also at the Mr Lock store. It’s probably worth shopping around to find the best price.
Of course if you are just starting out with your pet sitting business you can get away with using a simpler system of just a lock box and some key labels. These are both available from office supply stores.
To transport keys to and from visits I like to have keys stored in my purse in a zippable pocket. This makes sure that they can’t fall out and that I always have them with me (I don’t recommend leaving them in your car unattended).
If you are using sitters, make sure that after they complete the client visits that they return the keys to you for permanent storage. You don’t want to have keys left with sitters as you won’t be sure that they are securely stored, and you don’t want to be in a situation where the client calls and schedules and you can’t get in contact with your sitter or they are on vacation.
Your clients put their trust in you to protect their house and pets. Make sure that you honor this trust by storing their keys and personal information securely and responsibly.
You can get large rings that loop around and lock.
They allow you to slip the key rings onto the loop and keeps them more organized than in a bag.
Find them in a hardware store or locksmith shop.
I like the idea of a master key in addition to the original one.