Chris suggested this idea last night: Breakfast in a form you can eat in the shower. Good old Halfbakery has plenty of entries on the subject of breakfast, and even one on the subject of waterproof toast, but nothing on something that would meet your complete nutritional needs.
I'm envisioning a nutrition bar wrapped in fruit leather. It would be a little bit sticky when it got wet, but since you would be in the shower anyway, it wouldn't really matter. You could also sell a commuter mug that could hang from a suction hook on the wall of the shower (that wouldn't take any particular inventing, just a bit of marketing).
Come to think of it, you could just eat an apple or a whole sausage. Those are intrinsically waterproof. But where's the profit in that?
I really like the idea of the shower-travel mug. I´m always trying to drink tea or coffee in the shower and then it gets all diluted (if you keep it in the shower), or cold (if you put it on the tub-side table and forget about it).
A nice travel-shower mug with the Mary´s Great Ideas logo would be an excellent christmas gift, if anybody was trying to figure out what to give me. And if I weren´t so far away.