That isn't a bad idea, but it is pretty simple:
-Don't pack things you can buy cheaply/easily here. Pretty much everything you need for daily life can be bought here easily. Bring what you need to survive for a couple of weeks.
-Do bring a good towel. (You can buy good ones here, but they are not particularly cheap.)
-If you are a man and wear a size XL or above, pack as many dress clothes as you can get in there. Same if you are a woman over size M/L. Options will be limited.
-Bring small things from home you'll miss. Comfort food, a favorite book... Whatever you can use as a security blanket.
-An ereader is a good idea, if you like books. Otherwise you will be at the mercy of the bookshop's English section and the ALT book swap.
-Omiyage is completely optional. I brought it, lots of other people did, but by no means is it expected. If you do bring it, something small is best.
-If you are from the US or Canada, most of your electronics will be okay without an adapter, unless they have a three-prong plug. A couple of adapters for those are a good idea.
-Do bring portable electronics.
-I personally wouldn't bring a desktop, since you can build a new one here for a reasonable cost.
-Do rip your favorite TV series and movies and place them on a hard drive.
-Don't bring uncensored porn. (Apparently this was an issue a few years ago?)
-In the end, just think about what it takes for you to get through the day. If you think you need something specific, ask us and we'll tell you whether or not it is available or if you should bring it.