im using a corsair voyager 4gb.
washing machine proof, must be bomb proof tbh.
I have a Corsair Survivor. Slightly chunkier than your usual memory stick, but even tougher than the Voyager.
It's waterproof to 200m, made of CNC milled alluminium, and theres a site that
reviewed them that acutally boiled one on the stove for a couple of minutes then smacked it about with a hammer for a bit and it still worked.
Or if you want real ruggedness, you need a Pretec i-Disk BulletProof.
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Survives glancing blow from .44 magnum. .50 magnum, not so much.