I went to an emergency rescue lecture and they told me two must-haves, they are mostly for accidents.
#1 a tow strap at least 4" wide, 6" would be better, and at least 25' long, 30 is better. This is for dragging a horse out of a trailer if necessary, they also showed us how to do it. I also have one in the barn for the same reason. NEVER PULL THE HORSE BY THE LEGS, HEAD, OR TAIL.
#2 A roll of yellow caution tape. In case you have an accident, the first thing is to contain the area, keeps people out. Also if the horse gets loose, most horses now will relate the tape to electric fence, so it will contain the horse also.
The lecturer told several stories of the owners getting the terrified horse out of the trailer, only to have it get loose and run miles down the hwy.
I also never travel without a camping jug, 7 gallons, of water. I keep it filled and in the trailer, and empty it and refill before traveling. That way if I need to go in an emergency, I have water, stale water, but water.
One more thing I learned from the dealer that sold me my first trailer, Never let anyone else hook or unhook your trailer. I did a terrible thing once that could have been a horrific accident, but since I was the only one that hooks up my trailer, I would have only myself to blame. When I found out what I did, I literally got on my knees and said some prayers and thanked God that he was watching over me me that day.
that is the most sensable thing to do its like being a guard on a freight train checking all the waggons before you proceed.
As 2 people will not be garaneteed to check on the same things as the other.
Your the person that gives your self the certifacate of readyness to proceed that the trailer is correctley hitched brakeaway cable-chains and check your 5th wheel and make sure its locked in position connected and all electrical sockets pluged in and all correct.
It is a good thing to check with the trailers hand brake on that the 5th wheel is locked with a small movement forward to take the slack to veryfi the pin is home in the correct position.
And also every thing stowed away for the jerney.
Don't for get your personal safty equipment first aid kits ect.
Plenty of water hay and feed.
And extra clothing if you travle in winter.
Also make sure your hand brake released and all wheel schoches removed.
And the final check before departing is that all your lights work.