Besides my extra rope halter and lead rope, HYDRATION is very important to me, not only for myself but for my horse too...so, what do I take that holds LOTS of liquid?? My handy dandy Camel back, filled with ice cold water. Keeps my water cold all day and holds plenty for both me and boy..
Best thing about it is that it's not heavy and not cumbersome to haul around.
Since hubby and I are both nurses we're neurotic about safety, etc. So, I have come up with a pretty elaborate, yet compact first aid kit for our trail rides. I even have a first aid for horses book in it. I had to fight the urge to include everything I could possibly ever use - I would have needed an extra horse just to carry it. So I tried to stick to stuff I would need just to stabilize a person or horse initially until we could get them back home for further care. It fits in a large ziplock bag. Then I have a smaller ziplock bag with my "people comfort" supplies - chapstick, TP, matches, etc. I just keep both of these well stocked and in my saddle bag all the time, so I only have to pack food, etc. for each trip.
When we go on rides everyone involved has a saddle bag and usually me and my sister in law are the most prepared. I never leave with out my rope halter (and lead of course hehe), very small first aide kit, LOTS of water lol, hoof pick, those packets of cracker things lol I don't know what they are called, a camera, my cell phone and I think that's it haha.. Oh and sometimes a rain slicker :)
I'm bad... I don't take anything. Though we have a lot of dams/ponds around us so we can always find somewhere for the horse to drink. If it's like, alllll day then I have alittle drink bottle holder that clips to my saddle. But that's it. Oh and my mobile.