We might hope we never have to use it but horses being horses it’s very important to keep a small initial First Aid kit for emergency use. Remember to take it with you to competitions or whenever you are travelling your horse or pony anywhere. If you leave it hidden away in your tack room, then the day you need it will certainly be the day you are miles away from the yard. Talk to your vet about supplying you with the products that are prescription only (POM) such as anti-inflammatory powders or anti-bacterial creams.
Keep your First Aid kit in a robust plastic crate with a tight-fitting lid. That way all your kit will stay clean and dry, which is just how you need it when you come to use it!
Keep an eye on the condition of your kit. Check use-by dates on sterile compresses and bandages as well as creams etc. If you compete be aware that some creams and poultices may contain ingredients which could provoke a positive dope test!
Make sure you are happy about how to use all the various bandages, compresses and poultices in your kit. Practice your bandaging and poulticing skills before you need to use them. Maybe even investigate if your riding club runs equine first aid courses.
In any event ask for advice from your vet before administering anything other than basic first aid.