the same as usual, you should get a friend to feed them, alternativly you can get "holiday fish feeders" which are mecanical devices which drop a pre-determined food scource into your tank each day.
or add some goldfish/other cheap fish to keep them going.
but the amount is dependant on the number and size of your fish.
But don't worry, they won't die in 4 days, unless they are already in a bad way.
If it were me, I would toss in a bunch of feeders like Nate said but I would not put in dividers. You are only going to be gone 4 full days. Then I would do a 50 % water change when I got back. This will reduce any possible amonia or nitrite spike you might get from the added bio-load from the feeders. If I put in dividers, I would feed them before I left and then not until I returned and I would not put in feeders. 4 days is not that long to go without food, even for smaller ones.
These are all good ideas. 4 days isnt going to kill these guys even if they dont get there regular meal. I would feed them before I left and then as mentioned add some dithers/feeder fish that will occupy them until your return. They also sell those tablets at stores that are suppose to be good for on vacations, however i have never used them or read any input on them so I am not so certain to as how well they work.
i think you should tryto find someone to feed them for you or just feed them well before you go.a few months ago i went on vactaion for 5 days ,put awhole bunch of feeders in my tank,when i came back it was a messed.they ate some but just killed the others.stunk up the tank.best bet is to find someone
I would throw in a couple of feeders the day I was leaving if possible. Just enough for them to eat and not too many that would be left to foul up your tank.
I wouldn't worry about the four day leave. They can usually go for longer periods of time without eating. The problem with a friend feeding your fish is that they can make a mistake by overfeedging your fish. Unless it's someone who knows about P's