Honestly, leave everything at home. No watches, no electric razors, no writing materials. You don't need clothing, either. Everything you'll need is issued to you.
As for study materials, most validation tests were within the first 3 or 4 days, well before you get your first mail delivery (usually a week in). Higher level validation tests were about 10 days in.
Aim for mostly food in care packages, since you'll barely have time to even open the box and look inside, much less sort through a bunch of junk and supplies.
Regardless, you're not going to have time to study anything. You get 30 minutes per day to conduct personal business, though your "personal time" is mostly assigned tasks...shower, change, thought-of-the-day, laundry, learning menus. I never once had time to write a letter during those 30-minute spans, and had to wait until Sunday morning when you get about two hours to yourself.