Nowadays, an usb Key with 512Mo or 1g is not really expensive. However, if these capacities are too small for you, just buy a Kanguru Key. You have choice between 16, 32 and 64GB…enough to do a Back-up of your System. But big size is associated with big Prices. Actually, the 16GB costs $800, the 32GB $1500 and the 64GB $2800 (more expensive than a great computer…) !
Just dream…. :)