Cruise control is great on level terrain, but it's a FE killer on even shallow hills. I turn mine off during the part of my commute that's over a series of small hills.

Forget about drafting an SUV or 18-wheeler unless you're a NASCAR-caliber driver. It's way too dangerous.

If possible, start your trip in the wee hours (1:00-4:00 a.m.). That allows you to take advantage of relatively empty roads, and in warmer climates allows you to postpone using the A/C (another FE killer).

Learn from Jeff D.'s mistake -- avoid excessive food/beverage consumption. As "gonavy" notes, the more stops you make, the lower your FE.

Enjoy your trip!