Photo by ictsan (highly modified as allowed under the CC license).
I regret not having made up a cat first aid kit. Strictly speaking every cat caretaker should have one. I bet not many people have even got a human first aid kit! Anyway here is a list of items that might find their way into a cat first aid kit. This list is based on two sound sources: The Cat, Its Behavior, Nutrition & Health by Linda P Case and The Cat Owner's Home Veterinary Handbook by Drs Carlson and Giffin:
Veterinarian's phone number
Adhesive tape - for bandaging. An essential for a cat first aid kit.
Betadine solution - a topical antiseptic that helps to reduce bacteria that potentially can cause skin infection. It should be diluted 1:10 (10% strength in other words).
Cotton-tipped applicators - cleaning areas.
Eye dropper or oral syringe - for administering oral medications.
Flashlight - for better visibility.
Gauze pads - 3 x 3 inch
Gauze roll - 3 inch
Commercial Hairball remedy - to dislodge hairballs - example: Sherleys Hairball Remedy 100g (UK).
Hydrogen peroxide (3% strength) - for cleaning wounds and inducing vomiting (for poisoned cat). One teaspoon per five pounds of body weight every 10 mins. Repeat three times.
Linen cloth, sheet or blanket
Scalpel (I think this is doubtful for a cat first aid kit)
Scissors (blunt tipped)
Rectal thermometer - measure body temperature.
Petroleum jelly - to lubricate the thermometer.
Tripe antibiotic ointment - for bacterial infections (e.g. abscesses).
Ice pack and heat pack - for hypo and hyperthermia. And to treat contusions and to keep cat warm.
Blanket and/or heavy towel - to wrap and transport agitated cat.
Syprup of Ipecac - induce vomiting.
Activated charcoal - prevent absorption of ingested toxins. Veterinary advice needed. Mix one part to six parts cold water. Give four to eight teaspoons by mouth.
Dramamine - for motion sickness when travelling - give 12.5 mg one hour before travelling.
Pet pectate and/or Kaopectate - for diarrhea. This is an anti-diarrhea drug.
Metamucil powder for constipation. One to three teaspoons once or twice per day mixed into wet food.
Milk of magnesia - for constipation. One half of teaspoon per 5 pounds body weight. Once daily.
Panolog - ear drops.
Robitussin - for a cough. One quarter teaspoon per 5 pounds weight.
Antihistamines - for insect bites producing and allergic reaction.
Some of the drugs mention will be exclusively available in the USA but there will be UK and European or Asian equivalents.
This is a combination list for a Cat First Aid Kit from the books mentioned.
Pain relief should only be dealt with by a veterinarian as human drugs carry high risk of injury.