It is rarely possible to get a vet out within 10 minutes of an incident so having the basic supplies on hand until the vet arrives is important. I suppose the thing to consider is if the vet should be called, and when in doubt, CALL THE VET. If you are a new owner, start out with having the vet check out the horse(s) and establish a relationship with the clinic. Ask the vet about having Banamine and Bute on hand along with whatever else is advised. New owners need to educate themselves on care and what simptoms should trigger an alarm.
Really, every horse owner needs a good emergency kit on hand. We keep a kit in the trailer so we are never without.