I've recently sold four of my horses this past spring.
Each one went to their new owner with:
1. A folder with all medical information in it, papers, transfers, extended pedigree and a farrier/wormer rotation sheet for the time I owned them. The paperwork also indicated they had recently been trimmed and wormed.
2. Halter and matching lead.
3. Colour coded grooming bucket (matches the halter) with all their personal grooming tools in it (they are colour coded as well).
Many of the new owners were totally surprized they got so much with the purchase price. I figured these things belonged to the horse and should go with them, especially brushes. I don't use one horse's brushes on another.
A couple of people told me they never even got a halter with their horse the last time they bought one.
Ah well, that's just the way I am. What do you include when you sell your horse?