We'll start with Higher Standards Leather Care which has a 56 page thread on COTH full of fans. A nice stocking stuffer and everybody needs to clean their tack on occasion. You might as well support a few equestrian and use a product that smells good while doing it.
For stocking number two, everybody that shows needs a hairnet. We've all ended up with headaches and little dents in our foreheads from the knots on our hairnets. I discovered this product a few years ago and I'll never go back, not only that it's so durable mine has been around for several show seasons so it's well worth the price. Get one of these No Knot Hairnets for everyone on your list.
the hairnets are actually a little more expensive but they have a really cool option of a case for holding your hairnet that contains a mirror and comb! What a neat idea!
Here's another great stocking stuffer. I have several rope halters, I like using them for all sorts of horsemanship reasons (even riding in them) but I HATE messing with making the knot to secure them. Did I do it right? Is it going to come undone? This clever horse person has added a snap to her halters, making them simple and easy to put on. She has lots of custom options for all your needs. I like the wrapped (but not spiral wrapped) halter in purple with side pull rings!
Here's another great and useful gift idea, I have one of these Personalized lead ropes in green with Stanley's name on it. I've had it for years and the color on the lead rope and the embroidery has remained vibrant and unfrayed despite daily use. Great for boarding barns or going to shows, nobody will walk off with your leadrope again! Just $14.99 for an 8 foot lead rope (longer styles available) in your color choice with embroidery of your choice on the end. Nice solid snap as well!