During the week I'll ride out of the barn, those are generally 45min-1 hour depending on what I do. For the weekend it depends on what we have going on for how long we ride. I wont hook up to the trailer for anything less than two hours, just not worth it and we consider that a quick ride at the local park. Longer rides are in the 4-8 hour range and are worth a couple hour drive to get to.
How far you travel is dependent on you and your horse. I ran into a couple that were telling me of the trail they love to ride and it took them 4-5 hours. That got me excited as it was a place only 20 minutes away and right in my ball park. Since it was so close I drove up there in the car to take a look at trail maps and parking situation. Their favorite trail was 1.5 miles long so a 3 mile round trip! My horses wouldn't even break a sweat going full speed in that distance.
What to take:
-Full change of clothes, leave in your trailer/rig. Believe me there will be times you will want those to change into.
-Water, water, water and more water. Both in your saddle bags and in your rig, you'll be thirsty during and after a ride. Gatorade or such works nicely if you like that type of drink.
-Longer rides take something to snack on like trail mix, jerky, peanut butter crackers, etc. Stuff that packs a punch and travels well. Shorter rides you don't have to pack it with you but still a good idea to have it in your rig waiting for your return.
-Home made first aid kit. For your horses a maxi pad and tape make great bandages. Some people (men) shudder at the idea but it works. For you, bandages, motrin and aspirin. Motrin for swelling (falling off) and aspirin as a pain reliever. For both of you, neosporin or some bag balm in a zip lock baggie. Helps for those cuts.
-Fly spray for your horse, mosquito repellant for you.
-Twine or leather strips for repairs.
-Multi tool for repairs, can also double as your knife.
-Phone (keep it on your not your horse).
-I take along allergy medication, nothing ruins a ride more than a nasty sinus headache. If you are riding around the barn you already know what and when you'll be hit. Riding into strange areas at different elevations can get you hit hard.