Well, to help keep the thread from veering off again, I'll post something I bought for my tandem.

A Profile Design E-Pack. These are often called Bento Boxes, and are used a lot by triathletes. The idea is that with its placement on the top tube, aerodynamically shielded by the head and steering tube, its top-loading velcro closure allows a rider to gain one-handed access to bonk-preventing food and electrolytes (or cell phones or whatever).

It will work for the captain, but it might not work for many stokers, as if the stem attaches too low on the captain's seatpost, there may not be sufficient clearance between the stoker's stem and the top tube. A stoker has resort to a captain's saddlebag for the same purposes, but these generally close with a zipper, are not top-loading, and so are not so easily accessed.



The Bento Box TRZ model might work better for stokers, as it slopes downward as the stoker stem slopes upward.