Fish that are strong and healthy can survive a week without food. Feed them well until the day before you go then give them half the amount they would normally get and do a big water change and they will be fine.
I wouldnt go for the food block as its mainly ash and the fish wont eat it. It will pollute the tank and make the fish ill.
Isnt there a neighbour who you could trust to feed them? If they know nothing about fish then leave a small amount of food wrapped in foil and ask that one be given per day and that way they could maybe put the lights on and off for you to.