Collars and Harnesses
As soon as your cat starts to venture outside, they should be fitted with a collar and some form of identification. Make sure the collar is comfortable and loose enough to allow for easy movement - you should be able to fit two fingers underneath it while your cat is wearing it. You should also make sure the collar has a breakaway fastening, which allows it to break open if it becomes caught up in something, to prevent your cat getting tangled up!
There are a number of specialist collars on offer which have other helpful functions too - for example, some can combat fleas, while others reflect in the dark and even make a noise to alert small animals to your cat's presence - ideal if they keep bringing "gifts" home!
Before letting your cat out, you should also ensure they are micro-chipped, as this will make them much easier to find if they get lost.
It's important that your cats are able to play and explore outside, unless you have specific indoor breeds such as ragdoll cats. If you don't live in an area where you are confident that they will be safe, you can train cats to be walked using a lead. It's best to use a harness to allow for comfortable walking and evenly-distributed support should you need to pull them back.
Again, ensure that there is a comfortable fit, but that your cat is not able to slip itself out. You may find it helpful to put it on your cat around the house when you first purchase it, to get them used to it and so you can check for any problems in a safe space.