I've been gone for over a week and the fish were fine. (was out of state and a relative died, had to stay for the funeral) For 2 years I had to go out of state for 3-4 days at a time every 2 weeks, the fish never had any issues going without food for those periods. As a matter of fact, I came home to batches of fry several times after they were left alone without feedings .

Though I suppose it would depend on what kind of fish you have, I wouldn't trust some of the more carnivorous fish to behave themselves, they'd probably go hunting after the first day or two.
I'd say away from those drop in feeders, they just pollute the water. Auto feeders can be nice, but test it out ahead of time to make sure it doesn't dump too much food in at once. I have one but have never used it, it scoops up too much food even at the lowest setting.