I have hauled from Michigan to WV and back again, The first time I hauled a long distance I was a nervous wreck but I got better.

First aid kit, you hope you never need it but when you need it, you really need it.
I feed probiotics before and after a move.
extra halters and lead ropes
water from home, since my mare point blank refuses to drink when being trailered, I always wet down some hay and soak some beet pulp for her.
good directions
make sure and stop every couple hours to let the horse (and truck) rest, I don't unload since we usually are traveling on highways and having a loose horse in that situation would be potentially bad, but that way you can check on everything and offer water.
after a long haul let them stand a few minutes before you try to unload.
blankets if you are changing temps drastically, I don't blanket in the trailer generally because it is hard to monitor the horses temp.
the powdered quietex really helps take the edge off, my girl used to get really sweaty when trailering and I think that stuff helps take the edge off.

good luck!