Where will you be keeping the horse?
If it's at a livery yard then you do not need things like electric fending. If it's on part livery you don't need mucking out stuff, but on DIY you need the basics for mucking out (wheelbarrow, fork, scoop, brush, etc.) and looking after the horse like feed buckets, water buckets, hay nets.
For the horse you need: head collar/lead, grooming kit (soft brush, hard brush, mane/tail brush, hoof pick), tack (bridle, saddle if anyone rides him, numnah, lunging/long reining equipment as it may not be possible to keep him fit just driving, harness, cart), rugs if necessary, boots if necessary, travelling boots if necessary, first aid kit. Some small things like tack cleaner, fly spray, etc. but the rest you can pick up as and when you need them.
Other people on your yard can recommend a vet, a dentist and a farrier. You may want to do a worm test before you worm, but if you are on a yard they will have a worming schedule you need to fit into.
Is this your first horse? If you are not very experienced in buying horses it is always a good idea to take an experienced person (ideally your instructor) with you when viewing, and it's always a good idea to get the horse 5 stage vetted. If you are not prepared to cover possibly very expensive vet's fees take our insurance, but everyone should have Public Liability insurance no matter what.