1. A cheap click-type pen which can unscrew to refill the ballpoint. Unscrew it; there is room in here for a rolled-up $100 bill if rolled around the refill. Also, room for a big-eye sewing needle. Obviously, dont lose the pen!
2. A round metal bell -- the kind dancers from India wear on their ankles. I thread it with fishing line, and tie it to my rollaboard/briefcase. After setting it down, any movement causes the tinkle, which is not an obtrusive sound but distinctive enough for me to notice. The same bell can be hung on the doorknob inside your room if worried about night visitors. Add a couple more bells if you want; they are only about half-inch diameter. Or make two separate bell-lines.
3. The fishing line is also useful for many other things, especially when used with the big-eye needle.