Just went on a five week trip and was very nervous about leaving my fish under the supervision of non fish people.
On advise from this forum I bought medicine organizers and measured food for every day my friends were supposed to come in and feed the fish (I had food for two days, then skipped a day, so that the water parameters wouldn't be completely off due to possible overfeeding). After two weeks someone did a good cleaning and big water change, other than that they simply left the tanks alone.
All "feeders" said they REALLY appreciated the medicine organizers: it was easy to feed the fish, didn't feel they gave too little (my fish always behave like they haven't had food in months, so it is easy to think you should feed them just a little more) or too much.
All fish survived, the feeders were happy, it worked great and is so much cheaper than an automatic feeder (which wasn't an option anyways as I don't have the money to buy the 5 automatic feeders that people advised me to buy...).
You can leave fish without food for a week, but if you happen to have a pleco it might go and hunt for food and attach itself to one of your fishes...
Do NOT use the vacation blocks, they are really a TERRIBLE mess.
L.