Fish do not metabolize at nearly the rate mammals do so. They can easily handle 8 days--and longer. The feeder blocks are not recommended, as they will alter the chemistry of the water, which would be much more traumatic than a few days without food. Feed them as you normally would before you leave, and then walk out the door. They will be fine until you come back.
For what it's worth--I have 4 cherry barbs in a 5 gallon tank at work. Normally, the secretary feeds them when I am gone. Well, last time I was gone for a week, she was out sick. So, the fish were fed the Friday before I left, and then not again until the Monday I came back--9 full days between feedings. No deaths, no one even looked skinny. The smidgeon of algae that had started wass gone, though, and all the plants were clean and healthy.
