Hopefully it never happens, but if you run into a situation where your pet rat becomes injured or hurt in your home, you may want to have certain items on hand to deal with immediate emergencies. Certainly the number one recommendation is going to be to seek veterinary care. Either take your rat to your local emergency veterinary hospital, or contact your family veterinarian to see about getting them rushed right in, if something has happened, like an injury or a cut, or something that requires immediate care.
If you don't have the means to do that, it may be important to keep a few things on hand. One of those may be cotton swabs, that you can use to both, wipe out cuts or wounds, or also an opportunity to be able to look in their mouth. Another thing you may want to have are standard antibiotic ointments, like a triple antibiotic ointment like Neosporin, which used in small amounts are safe to use topically on a small lesion or a cut.
Sometimes rats may accidentally get their toenail caught in the bedding or in some part of the cage, and they can actually tear or damage their toenail. In that case, you're going to want to have a product called Quick Stop, that they sell in the pet stores, that you can pack on that area to get the blood to clot and get it to stop bleeding, should something like that happen.
Also a good thing to have on hand is sterile eyewash, sold over the counter at any drugstore. Sterile saline or eyewash products can rinse out cuts or lacerations. They can be used to rinse the eyes if your rat gets something in their eye.
Bandage material is somewhat tricky. It may require that you keep certain types of rolled gauze or cotton. If your pet gets injured and you need to do something temporary on your way to taking them to the veterinarian, then you may want to have some rolled gauze to cover a wound or a bandage, and also to prevent further bleeding.
But overall, most emergencies are going to require veterinary care. Most minor trauma, minor injuries, like broken toenails, minor cuts, maybe a small bite wound from a tussle with another rat can easily be handled at home by cleaning them, evaluating it, and then seeking veterinary care as appropriate.