The water bottle question comes up quite frequently with light aircraft as they can jam under the rudder pedals.
Check out GASIL or whatever the CAA call it these days, it usually has a report on a light aircraft having control difficulties due to jammed bottles.
Always a hazard in the summer in 150's/152's as they get incredibly hot, have poor vents and usually nowhere left to wedge a bottle safely.
However, I did hear rumours about some UK airlines banning bottles from the flight deck. Monarch or Air 2 perhaps, but just guessing. Anyone?