In order to make sure that the wizard holding you captive doesn't figure out what you're doing while he's gone, you'll have to hide all your items and spell ingredients. Remember that whenever he takes a trip, he's gone for an average of 30 minutes, so plan ahead and hide your items a good five minutes before he comes back. The only place to stash your stuff is underneath your bed, and the only things you can still have on you in your inventory that won't get you in trouble with the wizard are food items. Since he expects you to feed him dinner, things like meat and fruit aren't a big deal. Be aware though that you only have so many food items to feed him, so make the most out of every trip he takes to explore and gather materials. Once you run out of food, you're screwed. The first spell you should work on is the Transformation spell to turn him into a cat, that way you'll be free to explore at your own leisure.