Fly spray or other method of fly control
Feed and a way to store it
Saddle stand/rack with hook for bridle if you don't have bridle hooks (you can easily make both with stuff that may be laying around)
Lunge line (if your horse comes up lame, your vet will probably want to see it lunge as well as travel straight) and lunge whip if necessary
Sunblock or long nose fly mask if your horse has a white (pink) nose
Salt block and holder, or loose minerals and salt with appropriate feeder.
Jeans, breeches or Jods.
Boots, or other appropriate riding shoe.