Collect things slowly. Lease horses often come with their own gear, so that helps. Also every horse is slightly different in size so rather than buy things right now, put away that money you would buy those things for into a fund used only for horses. Add to it each month, and make a list of essentials. This would be my list
For the horse:
1. Hoof pic (The Ultimate Hoof Pic is worth the price)
4. Grooming brushes
5. Saddle (what type of saddle depends on what you want to do, but it must fit both the horse and the rider) and stirrup leathers/stirrups
6. Saddlepad(s) (Fit matches type of saddle used, may need more than one depending on fit of saddle and fitness of horse)
7. Bridle with reins and Bit (Which should be a bit that allows good communication and fits their mouth properly)
As for feeding:
1. Good quality hay (type depending on area and horse)
2. Haynet to put good quality hay in, to keep it off of the ground and make it last longer
3. Feed dish
4. Any supplements/loose minerals that improve horse health
5. Nutritional feed (depending on horse, could be as simple as alfalfa pellets or handful of pelleted feed)
1. Good fit helmet
3. Paddock boots and halfchaps, much easier to replace if they break or child grows
4. Breathable shirts, polos or the long sleeves with venting.
5. 'Horse socks' as in socks that are only used for the barn to avoid wearing any that are worn-out and can cause blisters
6. Good pair of gloves
For the home:
1. Horse-safe laundry detergent. My friend uses Dreft, I use Tide pods and rinse twice, dollar tree sells detergent that is seemingly horse-safe but I still double rinse, sensitive or odorless formulas are best
2. Good tack cleaner. Oddly enough Lather Therapy Wash from Tractor Supply works well.
3. Your horse's vet records, kept in a binder or file that is protected.
4. Horse towels, for drying your horse off or just using around the barn
5. Carrots/Apples/Alfalfa cubes/Peppermints as treats
1. A good vet, check them out and make sure they are well respected and knowledgeable
2. A good farrier, learn about hoof care so you can spot a good fit. Do not simply leave all the responsibility on your farrier
3. A good equine chiropractor, you need them at least once a year as your horse is an athlete and it can be very helpful.
4. A saddle fitter, but not always necessary if you have knowledgeable BO's or if you consult with the horseforum as well. They are few and far between it seems.
Final say: Watch your horse like a hawk, leased or not. Make observations in a notebook of their weight and overall health. They need to be wormed (consider a fecal analysis), vaccinated twice a year, and coggins pulled via collecting blood and analyzing. Subtle changes can often go unnoticed but they are very important as horses can be quite stoic.
Oh, yes. You should also create a first aid kit for the horse. Include duct tape, triple antibiotic, diaper rash cream, vet wrap, betadine scrub (NOT SOLUTION) to clean wounds, thermometer, weight tape, gauze, some form of antibiotic cream formulated for horses like furazone/wonder dust/etc) electrolytes, if you can afford it a stethoscope, scissors, cleaning sponges, bute, benadryl, list of contacts, completely blank check (for you to fill out to pay incase you don't have it on you), and extra leadrope/halter incase yours breaks or you are somewhere that is not near where you keep yours)
Obviously a long list, you can add what you think is best but I feel it's good to be prepared. It should also be a portable kit.
"Strength is the ability to use a muscle without tension"