Feed them well for a coupls days in a row before you leave (but don't overdo it) . Do a water change before you go as well. They will be fine without food for just a week. (And they'll be hungry when you get back :wink: )
Just got back from a week out of town. I slightly overfed my 25 cardinals + 5 guppies an left a few extra algae wafers for the shrimp/oto. Got back last night and everything was fine. I fed them their normal amount and they were all pretty excited. Also did a waterchange.
I leave my tank at school for 3 weeks during winter break and everything is fine when I come back. I still have 2 more weeks to go before I get back to them. If you have lots of plants and don't overstock then you should be fine because the fish can survive on whatever is living in the substrate and plants. I make sure to lower the temperature setting on the heater a little and reduce lighting to slow everything down.