Here's a place you'll probably be needing by now - the Akiba branch of Citibank. A haven for college students and tourists who go here and run out of money halfway, Citibank is the place to go and be seen thinking "I needed this money for food! Now what am I gonna do?"
The first time you go to Akihabara you'll spend too much money. It's a given, like how the sky is blue and how you'll get lost in the train system before you arrive. Don't let it bother you too much; if you survive your first trip, subsequent ones will be nowhere near as harmful to your wallet as you realize what's a ripoff and what's not.