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...
Step 3: Chitting
Put the tray somewhere nice and light - a windowsill is great as long as it is cool. My room is quite warm (As is under my sink where the eaters are) and they still work great there too.
Step 4: Chits!
If you found this instructable interesting and have diligently worked through every step, well done you. The alternative way of growing potatoes is below:
1) buy potatoes
2) dig hole in ground
3) put potato in ground
4) cover potato in soil
5) wait till plant has flowered
6) dig up avoiding poking your fork into the potato.]
As you can see, chitting isn't required - and I tried it last year with very little difference in quality, though chitting does seem to provide more quantity - perhaps because it is not caught in the early frosts.