If you lose your wallet while traveling in Tokyo, I would recommend searching thoroughly, and waiting a few days for a report before cancelling your cards. One time, I lost my bag with my wallet and cancelled all my cards for fear of fraudulent use. However, after making a report to the local police, my bag was found a couple days after, and none of my things had been tampered with. It turned out to be a major endeavor to get new cards sent to Japan after cancelling them, so I feel like I shouldn't have cancelled them in the first place. After all, credit card use is not extremely common in Japan, so it is unlikely that someone would go as far as to try and use an international card fraudulently.