I found a huge stack of 100Mb Zip disks in the back of a cupboard recently. The reader for them went ages ago, so I went down the plastic bag and a big hammer route. They were tougher than I expected and despite the bag I still wound up with bits all over the garage. Still, I feel fairly sure that no-one will be able to recover the data from them. No doubt an archeologist in 1,000 years time will excavate the landfill they're currently residing in and have a great time piecing them all together again - if they can find a machine to play them on!
Cheers,
TheOddOne