A guy wants to run a circuit to the rear of his property (700 feet)for lights on gate post. He also may build a garage back there at some point. First question - just run the 120/240 circuit (or feeder) the 700 feet with cable sized based on the volatge drop (I can't offhand think of any thing else. The other question is whether or not to run the feeder for the lights and future garage now. That is a question for the owner (whether he is sure he is going to build the garage at some point).
I agree with Chico. Assuming that this is a conduit job and he only wants the small circuit for the lights right now, I'd suggest increasing the conduit size so that the wires can be pulled out and replaced in the future. That wouldn't cost all that much to do today; and he gets to defer the garage decision for as long as he wants.
In fact I'd probably go up another trade size with the conduit just to make it easier on my back when I try to pull 700 feet of conductors out and back in.
Over that distance he will need 8 AWG to run 3.3 amps (assuming 400W of lighting) and be below 3% voltage drop. If he draws significantly more current (like for a garage), he's going to need a transformer and that may dictate a new service drop. As a result I would not bother with the "future needs" as they are most likely going be fundamentally different.
A small single phase transformer at each end will significantly reduce voltage drop and it is legal. By raising the voltage to 480 or even 600 volts at the supply end and lowering the voltage back down at the far end, the amperage and wire size is reduced. An overcurrent device at the far end would be required as well. You can still install a conduit sized for the future load, but install small conductors with perhaps two in ground open bottom junction boxes in the run to make the install easier. Comparing the cost of copper and the larger conduit to the cost of the two transformers will be useful in making a decision.
Also depends what all he wants in his garage. Lights and a garage door opener aren't all that intensive and going a few conduit sizes bigger is a great idea. If he wants to be welding car frames, though...
Funny thing about your situation. You run #8 for voltage drop and the next owner puts a 40 amp panel on it. Talk to the owner about the future and what your concerns are. At least then he will be less likely to do what I suggested. The next owner?? He'll probably try to sue you if he has a voltage problem on his 40 amp panel ;-)