|I mean, on what your schedule's gonna look like. If you're gonna spend all 6 days in Tokyo, then not much besides yourself and $$. You could even skip a majority of the packing if you wanted to buy in Tokyo, which can save you the luggage stress. Condomania sells more variety of rubbers than a Castle megastore in the states, with everything from the Madonna condom to 10 different varieties of safe dayglow condoms.|
(I love Condomania. Too bad I'm five years too late for the X Japan condoms)
If you are planning on seeing some of Japan while you're there, there is the JR rail pass which requires an advance purchase. For a 6 day trip, I doubt you'll want to get THAT much sightseeing in, but it's still something to consider before you go, as you can't buy it in Japan.
And my biiig huge piece of advice for a first-timer is: don't overpack. I guess maybe it's more of a female trait to do this, though I know I picked it up from my old man. But a lot of us worry-ers like being prepared and carrying 5 billion items we never use that we bring 'just in case' we might need it. I fucked myself over royally the first time I was to Tokyo doing this, because it's worse when you're 'goth' and you want to impress cosplayers. I brought six different pairs of shoes, bags of fake hair, plastic hair, yarn hair, wigs, makeup, skirts.. I brought enough in clothes to dress a dozen Japanese indies bands. Then there was food, because the rumour flies online that EVERYTHING is expensive in Japan, bla bla bla bla bla.
Well, long story, but I made it worse. Because I got to Shinjuku in rush hour and had culture shock so bad from all the people coming at me, from lugging my giant suitcase, three carry-ons and a purse down to the subnade, I was a nervous wreck. It took me 20 minutes to get 20 feet, I couldn't make it to my room that night, and they rented it out from under me. Totally extreme situation, but my point is; you can buy anything in Japan, it's really not THAT much more expensive, and if you're only there for 6 days you don't need to pack for a small army. ^^;