I am fortunate enough to live in a part of Japan that requires me to own a car, but for those of you who are traveling from abroad or don't own a car living in Japan, there are many rental companies that you can check out. Unfortunately car rentals in Japan are more on the expensive side, but I will tell you how to offset that in accommodations later on. If you are traveling in a group though, renting a car can be the economical solution. The driving law in Japan states that you must be 18 years or older to drive, and you are required to have either a Japanese drivers license or an international drivers permit to drive in Japan. You obtain a international drivers permit in your home country and it can be used up to a year from issue date; not from the date you arrive in Japan. Some of the more well known rental companies in Japan are Toyota Rentacar, Nippon Rentacar, Nissan Rentacar, and Times Car Rental. There are normally rental companies adjacent to airports so don't worry about not finding one if you are coming from abroad. Many of these companies have websites where youucan reserve a car ahead of time. The price of rentals vary depending on what type of car you want. Also considered if you will be driving in snowy areas as winter tires are a must in those areas. For more in-depth information on driving and rentals in Japan check out Japan Guides section on rental cars.
Gas stations come in two forms in japan full service (フル) and self service (セルフ). Pay close attention to which of these you pull into, because they differ vastly. Full service (フル) means that there will be an attendant there to fill up your gas tank. You will need to know a few Japanese terms to use full service. First tell the attendant what type of gasoline you want. Most everyone uses regular and you pronounce it re-gyu-raa (レギュラー). Next you had to ask how much gas you want put in and the easiest is to say is mantan (満タン) which mean fill it up all the way. Lastly you need to say how you are going to pay (cash, credit card). Credit car is credit card in Japanese and cash is genkin (現金). Using self service is more intimidating, but is more often found especially late a night. If you come from a country like America, you may be used to almost all gas station staying open 24/7. This is not true in Japan. Full serve all close and many close early (6 or 7pm). Even many self serve close; especially if you are in a smaller town. You can find more 24 hr self serve gas stations in you are near a larger town. There may even be a big sign announcing that they are open 24 hr. When using self serve there will be a touch screen. The first screen will ask you how you will be paying. (credit card = クレジットカード/ cash = 現金). The next screen will ask you if you have a members card. Push the button that has なし (don't have). The next screen will ask you what type of gas you want. Choose the one that says レギュラー (regular). Next you will be asked how much gas you want to be put in. Push mantan (満タン). The next screen will ask you to insert your money. Now you are ready to go. When you are putting the gas in your car you need to hold down the lever on the pump the entire time. If you used cash you, may have to go to a separate machine to get your change. It will have the word otsuri (おつり), which means change, on the ousdide. The is a barcode on the receipt you receive, and you scan that at the change machine. There is usually an attendant at self serve unless it's the middle of the night, so if you need any help just call them over.
If you are a resident of Japan this category has more options for you. As a resident you are able to sign up to use internet or manga cafes. These places are quite cheap 1200 - 2500 yen a night. There is an all you can drink drink bar. Sometimes all you can eat ice cream and you can order food. The food costs money though. Some internet cafe's offer showers for an additional price (around 300 yen). This option is only available to residents because you are required to sign up and give them your address. You receive a members card that you hand to the cashier at the front desk. There are many different internet cafe companies and some stick to only certain regions of Japan and some cover all of Japan. Here are a few that I use or know of. Copy and paste the Japanese or English into Google Maps to find locations.
Jiyū Kūkan (自遊空間)
Kaikatsu CLUB (快活CLUB)
Super Freaks (スーパフリクス)
Joy Cafe (ジョイ-カフェ)
For those of you traveling abroad there are still some great online resources you can use to stay in inexpensive but great hostels. Since you have access to a car you are not held down by choosing a hostel near public transportation. There are many day of deals you can get when booking last minute. The sites I use most often are Booking.com and Hostelworld. Hostel prices vary, but I've found hostels day of for around 2400 - 3200 yen. That's not too bad. Hostels also have many pamphlets for tourist areas around your hostel that you can use to find new and exciting places you may not have been able to find on your own on the internet. I know that's how I found out about some locations to visit. Make sure when you are booking online that the hostel you stay at has parking.
If you are visiting during a not overly hot or cold time of year, you can always sleep in your car at rest stops (mich no eki 道の駅) for free. They are scattered all over Japan and have restroom open 24/7. If you need inexpensive sleeping stuff (pillow, blanket) stop by a secondhand store. Once you are ready to leave you can sell the items back to them. Don't expect to get much money back though.
If you end up staying in a hostel many of them have a small kitchen you can use as you pleases if you get tired of eating out and just want a home cooked meal. Convenience stores are scattered all over Japan and are hard to miss. You can get quality food here and it is one of the few places that have public trash cans. I always go to convenience stores to throw away my trash while traveling. Always be aware of parking when you have a restaurant in mind. Parking is harder to find in Japan if you are in the inner cities.
Who want to brings wads of cash with them when they are traveling. That could be dangerous. It is quite simple to use certain ATMs in Japan, so you don't have to bring wads of cash with you on the plane. The 2 places I recommend to use are 7-Eleven and Japan Post Bank. Out of the 2, 7-Eleven is the most convenient as it never closes. The Japan Post Bank is usually located in post offices, so they close around 6pm on weekdays and may not even be open on the weekends! Even with the inconvenience, both of these ATMs accept foreign cards. Japan is a cash based society so you should always have some cash on you. Your credit card may not be accepted at many place.
Laundromats do exist in Japan they just aren't called laundromats; they are called coin laundry (コインランドリー). There seems to be at least one coin laundry in each town I drove through. To find one copy and paste the Japanese into google maps and you should be fine. In the coin laundry you have washers, old looking dryers and washer/dryer combos. As it's called coin laundry you can only pay in coins. Also if you stay at hostels there is a high chance that they have a washer and dryer. You may have to pay to use them at hostels though.
There are a few options you have available concerning wifi in Japan. First off there is not much free wi-fi available in Japan. The free ones that I use most often are at Starbucks, McDonalds, and Aeon Mall. Aeon Mall is a chain of malls throughout Japan. They are hard to miss. These 3 places have free wifi that is easy to connect to. If you want a constant source of wi-fi you have a few options. First you can get a SIM card for your phone. I believe you can find SIM cards in vending machines in airports. You can also rent a pocket wifi. This allows you to hook up many of you devices to a mini wi-fi box. I've used pocket wi-fi for my phone and laptop. I've also use a SIM card and then used the hotspot on my iPhone to use my laptop.
Now that you have these tips, you can start planning that dream vacation to Japan at your own pace.