I went for a very short ride yesterday on a circular trail - I went 4 miles. I had 2 bottles of water, a hoof pick, a pocket knife, cell phone, camera. I was taking my GPS but let the dang batteries.
I was never further than 3/4 of mile from the vehicle on this particular ride as it is a ride on a loop. If I am riding up at Ebenezer I would have
Heart Monitor on Biscuit
GPS WITH the batteries
Toilet paper (which is funny - I rarely get off on the trail but have it just in case!)
Little first aid kit
Snack of some kind
If I know it's going to be a longer/full-day ride, I will pack something for lunch/snack, a couple of bottles of water, knife, cell phone, camera, some little first-aid and anti-bug items for myself and the horse, extra bits of leather in case I need to make an emergency tack repair. I may or may not bring the horse-collar and lead rope with me. It's nice to have along if we take some extended breaks. I can just put the collar on my horse when I tie him and take the bridle off entirely, so he is free to scratch his head without the worry of him rubbing the bridle on a tree or tie-post and breaking it.
I'm one of those "everything but the kitchen sink" types.. ha I've really never had to use some the stuff I drag along, but I've been in situations where others who were not as prepared needed something.
Tied on top of my bags
Sweatshirt or rain slicker
Rope halter and leadrope
In the "dry" side
Shoelace/twine/strips of leather
Duct tape (small roll)
Camera (when I remember it..)
Mini first-aid kit (QuikClot, Vetwrap, gauze roll, alcohol, antibiotic ointment)
In the "wet" side
Sandwhich(s)-- Depending on who is with or carrying bags)
Apples (for the horses.. Usually.. ha)
Ice pack(s) (also available for emergency use)
Water (however much I can bring to balance out the bags)
I haven't gone out on any rides that are longer than 3 or 4 hours, and have usually just brought along water for me, my cell phone and had my horses' halter on underneath the headstall w/ lead rope attached.
I want to buy some saddle bags though and pack it with some stuff that will always remain in there - first aid kit, hoof pick, extra pair of reins, etc. I don't get out and trail ride a lot, but you never know when you might need something.