Fill the fuel tank,change the oil and filter and if sitting in a garage maybe put 1/2 plywood under all the tires. If you don't have a good charger like OH48lt stated take the truck out maybe in January and run her for about 20 miles at highway speeds.
As far as fuel isn't all diesel #1 now a days. The refineries may change to a winter blend as in adding anti-gelling agents but other then that all ULSD road fuel is the same.
And if anyone thinks there is not any water in their tank they are kidding themselves. You may not have a lot but I assure you, if your truck is a year old you have some water in it.
Link Don