All products listed here are things we have used to great success and are not sponsored or paid advertisements.
One of the most indispensable items to me are the pheromone diffusers. They mimic the pheromones that a mother kitten uses to help calm her young kittens, It is both drug free and natural. From experience I can say they do help with things like helping a kitten to acclimate to a new home more quickly. They can also help with reducing behavioral problems such as inappropriate scratching and fighting with other cats.
Every kitten goes home with one of the collars but setting up the diffusers a week or two before your new kitten comes home can help make the transition easier for them.
One of my favorite training aids is the SSScat. It is really good for teaching the kitties where they can and can't go. Also very useful for training them to not try and go outside on their own. One of the really good things with it is that because it triggers without you being around it shows them that they don't only have to follow the rules when you are around. It also means that when they try to go somewhere they shouldn't and it triggers you aren't the bad guy which helps to keep your relationship with your kitten strong.
Without fail this is the kittens favorite toy every single litter. All I have to do is open the drawer that I keep it in and every one of the cats comes running in the hopes that I am pulling out Da Bird to play. Just make sure to clear the area where you plan to play in because sometimes the cats get so focused on the toy that they don't pay attention to what is near it and sometimes will run into something in their attempts to try and catch it. You can also buy refill feathers for it for usually around $5 at local pet stores.
This is my favorite harness and the one I use when I take my kitties out for walks. Due to the way it fits it is a lot more comfortable for the cats to wear and in my experience it helps prevent cats from pretending they just had a huge weight put on them. It also goes on and comes over very quickly and easily while also being near impossible for a cat to slip out of as long as it is on correctly and you are paying attention to your cat.
I pair this harness with the Come With Me Kitty bungee leash that comes with the Come With Me Kitty harness. I don't use the Come With Me Kitty harness at all but I love the leash because it is made for cats so it is springy enough to extend with a cat instead of just pulling them. This allows me to give a gentle tug in the direction I want to go without actualy tugging on the kitty.
What I love about this cardboard scratcher the most is that unlike the cheap $10-20 ones you buy at most pet stores and need to be replaced every month this one here doesn't fall apart so easily. The last one I got lasted two years before I replaced it. Also because it doesn't fall apart so easily there is a lot less mess to clean up. With the cheap ones I am finding bits of cardboard all over the house as it falls apart. But The Pet Fusion scratchers use a high quality cardboard that doesn't fall to pieces from light scratching The cats also tend to enjoy resting on this making it serve as a ct bed as well.
This feeder has changed the way I feed my cats. It does have a few negatives but overall I love it. The built in scales mean that I can monitor how much each kitty is eating and when the vet asks if their eating habits have changed recently I can look it up and answer i it definitively. The bowls clean up so easily with just a little warm water. And for the kitties that overeat I can tell it how much I want to feed and it will light up and show me when I have hit that weight. It also means I can ensure that cats that need a special diet can't get much of the food they shouldn't be eating. It even has an intruder mode that detects when a cat whose microchip isn't allowed with that bowl it will shut the door to block them out. But only if you contact the company and ask them to activate Intruder mode or Fast Intruder mode which closes the door faster. I do wish they would make it an option you could set the modes yourself without needing them. But I understnad that it is partially a safety issue. I will have a much more indepth review soon but overall this is a real winner for me.