The Otter Box will keep your things dry. Starting with the 1000 series which will fit in most BA pockets to the larger 3250 to keep your Camera, MP3 player and phone dry.  You won't be able to fit an Otter in there.

What they say :

The OtterBox Series are waterproof, crushproof AND watertight (it floats!). These cases are perfect for protecting your valuables from the elements, whatever they may be. The OtterBox is a patented drybox designed to handle full submersions--up to 100 feet!

Otterbox 1000 Series Exterior Dimensions: 4.837" x 3.682" x 1.652"  Internal Dimensions: 3.700" x 2.350" x 1.000" 

Otterbox 2000 Series Exterior Dimensions: 6.855" x 4.571" x 1.829"  Interior Dimensions: 5.757" x 3.140" x 0.979"

Otterbox 2500 Series Exterior Dimensions: 6.855" x 4.563" x 3.590" Interior Dimensions: 5.691" x 3.063" x 2.741"