Besides getting your horse ready be sure you are.
Things to take or have ready:
Give yourself and your horse a spray of insect repellent. Apply some sunblock and take some with you. In your saddle bag suggestions:
Hard candy like Jolly Ranchers
Bandanna for multiple uses like wetting to cool yourself and your horse down
Granola bars (some that your horse will like too)
Camera (check batteries)
GPS (again check batteries)
Wet Wipes- They sell small individually wrapped towelettes that are nice to have in your pack for washing hands or potty emergencys.
Bug repellent towelettes for you and your horse if you need to reapply
Hat or Helmet
I think that's pretty much my short list of whats either in my pack or ready to go at any time
Be sure to have fun!