Fish can easily go a week without food. If you're only going to be gone 4 days, just feed them a normal amount the day you leave (don't throw in a lot as the leftover will decay and cause excess ammonia). They will be fine till you get back.
Definitely stay away from the feeder blocks. They really don't have a lot of food in them and are mostly chalk or plaster or whatever holds them together. The automatic feeders work but are risky. If the happen to malfunction and dump way too much food in, the ammonia spike could kill all your fish.
If you feel you have to feed them, find someone to come over the 2nd or 3rd day and do it. Measure out what you would normall feed them and put it in a cup on top of the tank. All they have to to is pour it in. Hide the food so they can't feed extra if they think your normal amount isn't enough.
There is an advantage to not feeding. No food means they produce very little waste. With little waste to process, even if a filter happens to quit working, the ammonia buildup won't be enough to harm the fish.