1) Potatoes - not just any though!
2) egg box
4) 'special knowledge' (you'll get that in a minute...)
Step 1: Buying the potatoes
You can pick them up fairly cheaply from a good shop - mine here cost Â£2 from the local nursery
More importantly is that you can often pick up varieties of potato not usually available or even endangered or rare plants - though often these are sold as actual plants rather than the rare and valuable tubers.
Step 2: Learning the knowledge...
Look at my blurry photo below (Damn my nokia n95 which I've been using for all my grow your own series pics)
See the knobby bits - commonly called 'eyes' - these are where the potato sprouts from. As far as you are concerned this is 'up'. Welcome to the potato grower brotherhood...