Depending on the type of container they are in, you could doctor his toothpaste, shampoo and conditioner. Habanero in the toothpaste, mineral oil in the shampoo, and Nair in the conditioner bottle are some evil thoughts that come to mind.
Love the catfood/tuna trick (files that away for friend's house).
What about using a water-soluble glue to glue some stuff in place? A little elmer's glue could pin keys to counters, shoes to the porch, sunglasses closed, wallet closed, razor to stand, glasses to nighttable, etc. Soaking in warm water will dissolve the bond, but yanking free might damage one or both surfaces, so you may want to be judicious.
Since you will be replacing his alarm clock with yours, why not locate yours across his room that you have unscrewed the lightbulbs from and rearranged the furniture in. Nothing more disorienting than a klaxon driving you to stumble through an unfamiliar room in the dark.
Everyone is entitled to be stupid, but some abuse the privilege.