The following items assembled into an emergency kit will help you handle most situations. Discuss this list with your own veterinarian, he/she may have other suggestions that are appropriate for you and your situation:
All medications should be given at the advice of your veterinarian or the veterinarian treating the condition. IMPROPER USE OF TRANQUILIZERS AND OTHER MEDICATIONS CAN RESULT IN THE LOSS OF YOUR HORSE.
Source: Neva Kittrell Scheve & Dr. James Hamilton, DMV