Ditto on the whole bale of hay.  I always take extra and bring home what he didn't eat.  I also take some alfalfa to entice him to eat if he's feeling fussy...  he used to go off his feed after along trip and the alfalfa would get his appetite back on track.  Just a flake added to his normal hay would be enough. 

Oh, and if you can, bring water from home.  Some horses won't readily drink water that is not from home.  I have a 39 gallon horse water tank in my trailer and always take water to rides, jsut in case.

Pack two bales to be safe. 

Hay is the best babysitter.  you may want to walk away and get a hot dog.

You will want to have a hay net for your horse during the day.  Most likely you will fill a manger of some sort in your trailer for the ride to and from. 

So many times I bring too much hay and to find out it was just enough.  Seems my guys eat more on the road.  Hey so don't I :)

 Have Fun!

One trick I learned about horses who are finicky about drinking foreign water is to sprinkle strawberry jello in their water at home.  When they get used to the smell of the jello, it is easy to doctor the water from wherever you might be, and your horse won't know the difference.  It only takes a small sprinkle.  Just enough for your horse to smell.

Marla

I've done that water trick, too.. Only with mint extract.. My picky mare likes it and she is strange about what she will or will not drink.. She may refuse water in one bucket, only to drink the same water in another bucket..

That's my girl....

Both hay and water are very important when you travel with your horses. 

We camp frequently and have learned that the more your horse becomes accustomed to drinking away from home the more they will.

Kinda like you and me we have our habits too.

Local to our property we have running water and ponds.  We are always encouraging our horses to drink on local trail rides.  This has taught our horses that it is okay to drink elsewhere besides their special red bucket (spoiled brats all have their own matching colors).

There have been places we have gone that the horse actually turns away from a water source.  Trust the horse it may be foul.  Although my qtr horse prefers a muddy puddle in the paddock over his water trough.

I would suggest bringing water from the barn the horse is stabled in. But I see you are traveling in the winter.  However, Walmart sells inexpensive Blue water containers.  And I still stick to more hay is better.  Don't take the chance.  I have had to find hay one time too many to make me learn to carry more than I need.