Usually when I go on business trips (anywhere from one to 4 nights usually) I ask my roommate to throw the easy ones some food...but if she forgets its totally ok. Like Delta said, most fish can last 10+ day's w/o food. In the wild fish frequently go w/o food for several days and then eat really well for a day etc. (of course there are some, esp fry who need food constantly through out the day) No one feeds them once or twice a day. Now of course the fish we have are conditioned to those regular feedings...so I make a point of feeding them some extra the few days before I leave, and making sure I skip a day or two every week or every other week so they're familiar with picking up all the extra food off the bottom or out of the plants etc.
So, I'd second the "dont worry about the feeder block" sentiment. There are also automatic feeders you can buy at the lfs...I've never tried one, but some people have said that they're really nice to use, you might take a look at them. Oh, and also last time I went to buy a feeder block I actually read the package and it says that feeder blocks may not disentigrate at a good pace except under certain conditions...and the temperature/pH where I keep my tanks is not in those certain conditions. So if you go for those blocks...make a point of reading the package.