I picked up Lonely Planet's guide to Tokyo which actually included one page (out of 272) headed 'Tokyo for free'! I now feel armed to take on the scary $$$$ Japanese world. Actually, it seems like a very good/fun guide - Cat, it includes a breakout box on 'Cosplay'!!
Friends have already started banding around to suggest 'survival food' products to bring with me. These include rice and couscous mixes, muesli bars, porridge and other oat concoctions, noodles etc. Tins are going to be prohibitively expensive, but sealed dried fruit could be ok. And a large jar of vitamin supplements.