I haven't read through the posts, so I'm sorry if I sound repetitive.
I would get a saddle bag and fill it with emergency supplies for you and your horse. Just enough so if either of you were to get hurt you could buy yourself time to call for help and whatnot. I would also always make sure to pack a lot of water and some candy and trail mix, especially on the really long trails. You may want to look online and think about what emergency supplies other than medical you deem important to take with you. An emergency whistle, mirror, or strong flashlight (if I remeber correctly) can all be used to signal for help if anything would ever happen to your cell phone. Basically three of anything means "I need help". You might also want to consider keeping some matches in a baggie or other waterproof container. They take like a centimeter of room in any bag and they're great to have for emergencies. Again, I would go online and read about preperation for hiking. I know you're riding but most articles have really good tips you can use for any outdoor venture.
I would also ALWAYS ALWAYS tell someone or leave a note detailing exactly where you plan to go. Just in case you get hurt and can't call anyone (for example, you get knocked out). Then people will know where to find you.
I know I probably sound weird but it's better safe than sorry and you never know what could happen
. You did mention where you live, I can't remember exactly where right now but I'm sure you know some of this already.
Good luck and I hope I helped!