Properly inflated tires provide a noticeable improvement in my fuel economy.
I get near the same mpg out of my '03 Honda Odyssey which is considerably heavier than your Focus.

If you can keep a constant speed around the buggies, or coast to manage your speed, then your heat loss in braking will be reduced.
As you are well aware, the Focus has a sweet spot for fuel consumption which should be right around your travel speed on two lane roads.

Coast when you can, brake when you must, anticipate your speed changes or your mileage will go bust.