This is all taken care of for you! Soon after your arrive in Nagoya, our supervisors in the Kyoikukan, a.k.a. "the Office Boys", will walk you through the paperwork needed to get a bank account and an ATM card with UFJ Bank. You'll be able to withdraw money from your account as soon as there's some money in it, which will be after your first payday on August 18.
To tide you over until August 18, you'll need to bring some money with you (see Money). This money you bring is probably best transported by travelers' checks which are safe, relatively convenient, and which offer a slightly better rate than cash.
As for credit cards, they are not as widely used in Japan as back home. But they are more widely used now than a few years ago. It is well worth bringing a credit card for vacations, emergencies, and internet purchases, if nothing else.
While in Japan, you may have bills to pay back home, such as student loans. The Japanese don't use checks, and electronic payments so far cannot be made internationally from your Japanese bank account. The easiest thing to do is to periodically send sums of money from your Japanese bank account to your bank account back home, and then write checks from your bank account in your home country.
Lloyds bank's Overseas Remittance Service offers an easy way to do this. When setting up your account, Lloyds will ask you for your home bank's address, branch number, and electronic routing number, as well your account number. You can save time and effort later by getting this information now before you leave. Once it's all set up, you can transfer up to ¥5,000,000 per month from any UFJ ATM in the country. It's about as easy as it gets.
There are other ways to send money home as well, such as money orders from the post office. You'll learn about these in your in-service training seminars in August.