Is he going to live in your "backyard?" Do you have a stall and fenced in turnout? If so, you'll need things to clean up after him. A basic wheelbarrow, a shovel (I prefer what's called a "grain shovel"), a rake, some people prefer a manure rake, and a place to store hay, bedding, and grain (Metal trash cans are the cheapest and best option for that.) Also, whether you board or have him on your property you need some kind of tack box. The best buy I've found is this, at WalMart: Sterilite Plastic Footlocker - Walmart.com
This is the online
price, for 2. You can buy one at the store for $20.00
If you buy leather tack you will need to keep it cleaned and oiled. Check on posts here and make your own decisions on products.
You will need one basic blanket. I watch mine (5 blankets/sheets for 3 horses) gather dust every year, BUT the one time you need it is NOT when you're running around town looking for one instead of nursing your sick horse. Been there, done that. Measure your horse's girth for sizing. Your guy could be as big as mine (big head, 16'3hh) and he is 84" around, which is 7 feet at the girth. Buy it in March/April, when the online stores and farm supply stores are clearancing them out. They don't have storage, you see, so they buy new winter stock every winter. If your horse is OTTB he's been blanketed before, but introduce it to him as if it is new and scary when you buy it, just to be sure.
Get online and find horse suppliers. Everybody has their favorites but mine are Horseloverz and StateLineTack. I've been buying from them for decades, now. You can keep your horse supply costs down by chasing sales there. Congratulations! Now, you'll never spend another minute channel-surfing looking for something to DO!