I'm planning how I'll be bringing my money in my future Japan trip, and I was wondering if I could use a mix of cash and credit cards. Sadly, as of the moment, I only have an Amex credit card.
Also, if I could, would you recommend it? (in regards to additional fees or anything)
Credit cards are definitely NOT widely accepted in Japan. It was slightly better than I'd heard - I'd heard not at all, but I went last year (including Osaka).
Essentially, it was easiest to take some cash (As much as you're willing to have on your person), and then go to either a post office or 7-Eleven shops - they have ATMs that allow you to use foreign credit cards or debit cards, including American Express (Source: personal experience, and another source online).
I found that the most convenient, I just accept the fees and get a decent chunk out at the time, while my travelling friends exchanged a much larger amount in Australia and brought the cash with them.
Each to their own. I dislike having large sums of cash on me :/ Note that several banks allow you to get fee-free cards for travel. I also used the Qantas Cash credit card - it's a Visa card, but allows you to pre-load it with foreign currencies (like yen) and then draw on that (earning airpoints at the same time).
Qualifier: I live in Tokyo.
All the large stores, especially the major electronics retailers and any international-level hotel, will accept most credit cards. American Express is certainly the least popular, if you can obtain a Visa you'd have very few problems.
Smaller stores, almost all restaurants under $50/plate (and some that are over), and the smaller non-chain hotels are cash only.
On the positive side, withdrawing cash from an ATM is much easier than only a few years ago. 7-11 convenience store ATMs accept Plus-network bank cards, so if it has the Plus logo on the back you just need to find a 7-11, and that won't be a problem.
Fees are $2 per transaction over whatever your bank charges, so don't go in for an extra $20. I usually withdraw Y50,000 - Y90,000 at a time.
Mark's answer is generally correct -- Japan is still a cash society and it is generally far more convenient (and reliable) to carry a wad of cash easily withdrawn from a 7-11 or Japan Post Office ATM -- yet credit card acceptance is far far better than the dire picture he paints.
Places that almost universally (90%+) accept credit cards:
Places that generally (50%+) accept credit cards:
Of the places that do accept credit cards, Amex is definitely lowest on the list. Visa and Mastercard are almost universally accepted. Japan Diner's Club or something of the sort (you likely don't have one) are less accepted. American Express probably runs around 50% of Visa/MC.
So if you're planning on paying for everything with your Amex, you're going to run in to some trouble. If you are planning to use it in the first list of places (mostly for larger purchases), you'll have better luck, but will probably run in to somewhere that doesn't accept them.
The above is my experience living in urban/semi-urban Western Japan for the past decade and change. Your mileage may vary if you go out to the countryside.
