Fetish Pony
Equipment
Clothing: Due to the laws in the US restricting public nudity, some sort of clothing is always recommended for all ponies. In extremely private settings, full or partial nudity may be acceptable. Many ponies enjoy full latex or spandex body suits, while others just work out in shorts and a t-shirt.
A blanket is also a good idea for ponies for two reasons. First, to keep them warm in the colder weather. Second, when they are done with a workout, a small breeze over sweaty flesh can be very cold, and it is a good idea to keep your pony as warm and dry as possible.
Tack: The tack I'm going to divide into three categories, Basic, Intermediate, and Advanced, but please note that these are my personal classifications, and not necessarily considered so everywhere.

Basic:
  1. Bit: The most basic bit can be found is most fetish shops, and even a few sex stores. Some people choose to have a bit and bridle come together, though its not necessary.
  2. Reins/Lead Rope: These can sometimes be created from things you have around the house or found in equestrian stores and fetish shops. What I've also found works well are matching dog leashes in six foot lengths, which you can find in leather or nylon in any pet store.
  3. Tail: Simple butt-plug tails can be found as a novelty item in most adult or fetish shops. Most of these are not real horsehair, but get the point across. Searching the web or making one yourself would probably be the easier route if you want a real horsehair tail or one that is just attached to a harness instead of a butt-plug.

Intermediate:
  1. Arm restraints: These can be anything from sleeves to wrist cuffs. Please be extremely careful when you begin to use these on a pony, as it compromises most ponies usual ability to balance and they could get hurt.
  2. Bridles: I'm putting these in the intermediate category because of the extra head coverage. They can be found in many styles from the basic to the full pony head. They are also useful for ponies who are unable to have a bit in their mouth.
  3. Plumes: These also get in the intermediate category because you need some sort of bridle to attach it too!! They come in a variety of styles and colors to add a little "flash".
  4. Harness: These are absolutely not a necessity for all ponies, never assume that this (or any tack) is a must have. However, most good pony harnesses feature a wide belt or corset arond the middle as well as genital and shoulder straps. D-rings at the shoulders are also a suggested addition for reins on cart ponies.
  5. Saddle: Many four-legged ponies, and even some two-legged ponies love their saddles and provide a comfy spot for the rider to sit, or just as decoration. I've heard that the best saddles are small, real pony saddles, but you can also buy human pony saddles if you find the right dealer online. Here also, note that for two-legged ponies, you have the option of a saddle for your back, or a custom/modified saddle for the shoulders (for the two-legged shoulder-riding ponies). Use whatever makes you comfortable.
  6. Stirrups: I'm putting these here to go along with the saddle, though just because you have a saddle does not mean you need stirrups, and just because you have stirrups does not mean you need a saddle.

Advanced:
  1. Martingales: Martingales are straps from the bridle to harness to reduce "spirited" behavior (i.e. head movement) but should only be used on very advanced and highly trained ponies.
  2. Blinders/Blinkers: Blinders can be attached to the bridle and should be used with advanced ponies due to the limitations to the pony's vision.
  3. Spurs: I'm only putting these in the advanced category because you CAN hurt your pony if they're used incorrectly.
  4. Hooves: Hooves can be a fun addition to any pony, but they can also be extremely dangerous. Know your limitations and use common sense. Sprained or broken ankles can and do happen.