This one you can leave for last; basically you need to feed every food and food combo in the main DLC. Also, you can go like "Guest House 1" and pick up food and food combos and find Jack, then end the trial and start a new trial like "Testing Area 1" and so on until you give Jack all the food. The game keeps track of the food you gave Jack, so here's the list:
Spice
Cheap Wine
Chicken
Chicken + Spice = Spicy Chicken
Garbage
Beer
Fruit
Beer + Fruit = Fruit Beer
Dulvey Cru
Cheese
Stew
Cheese + Stew = Cheese Fondue
Spice + Stew = Tom Yum
Cake
Sugar
Cheese + Cake = Cheesecake
Sugar + Cake = Sugar Cake
Fruit + Cake = Fruit Cake
Garbage + Sugar = Baker Family Special