The gadget shops around Akihabara are pretty stunning. Be aware that most of them sell racks of porn as well.
Go at the crack of dawn (like a bit before 5.30am) any day for the tuna auction, get a bowl of tuna sashimi at a stall, and then go take a nap at the hamarikyu botanical gardens nearby.
After you've seen the tuna auctions at Tsukiji, wander over here as it opens and get the garden all to yourself. Take a nap in the middle of it.
