Encourage your sitter to feel at home
Avoid dangerous molds or critters getting to your perishable food by having your
poor college student house-sitter eat it. Instead of thinking "I better toss this because it'll go bad while I'm gone" and frantically emptying your fridge, your sitter can take care of that for you by nourishing himself. This will also produce some trash/recycling/compost to go out to the curb, maintaining the appearance that things are business-as-usual at your home sweet home.