The contents of kits will vary, due to personal preference, but there are some basic supplies that should not to be overlooked. It is vital that you have first aid supplies close at hand. They should be kept in a handy and easy to access location. Familiarize yourself with the contents of your first aid kit and know how to use them. For the container itself, a plastic tool box with a tray on top is a great way to transport your first aid supplies.
Most discount stores have various sturdy plastic tool boxes that can be had at a reasonable fee.
I have found that I prefer the bright red or yellow ones, so they are easy to locate. Just make sure it's big enough for all of your supplies. This way if you have to send someone to fetch the container they are in no doubt that they have located the correct item. You may also want to have a more portable version, as it is a good idea to carry a kit with you when you are out on trail rides, horse camping, or are otherwise in a situation where veterinary attention is not readily available. Make sure it is a waterproof, nylon bag with a zipper and covering flap make good choices.