お好み焼き(Okonomi-yaki)
広島お好み焼き(Hiroshima-style Okonomi-yaki)
焼きそば(Yaki-soba)
たこ焼き(Tako-yaki)
焼き鳥(Yaki-tori)
甘酒(Amazake)
Amazake might look like Sake but it's not. It doesn't include alcohol in it so it's a child-safe drink. It's basically just a sweet rice juice. It's definitely worthy to try for anyone!
梅酒(Ume-shu)
Basically a plum(Ume) sake. It's somewhat sweet and somewhat bitter at the same time. Ume might be a bit acquiring taste for you, but if you want to experience Japanese things and you like alcohol, Ume-shu is the thing you can't miss! Personally, this is my favorite alcohol on earth though I don't drink at all.
ラーメン(Ramen)
二郎系ラーメン(Jiro-style Ramen)
餃子(Gyoza)
Originally came from China around 400 years ago, but the Japanese version is a bit different from the original. (The original Chinese version is basically boiled without being cooked and has a thicker skin)
At ramen restaurants, many Japanese customers would order gyoza and ramen at the same time for some reason, but you will know the reason for some reason if you just try it.
カツ丼(Katsu-don)
天丼(Ten-don)
牛丼(Gyu-don)
豚丼(Buta-don)
うな重(Una-jyu)
海鮮丼(Kaisen-don)
鉄火丼(Tekka-don)
回転寿司(Kaiten-Zushi)
オムライス(Omu-rice)
カレーオムライス(Curry-omu-rice)
カレーライス(Curry-rice)
焼きカレー(Yaki-curry)
そば(Soba)
うどん(Udon)
おにぎり(Onigiri)
Onigiri is a very simple fast food in Japan. At any conbini(Japanese convenience stores), you can buy various kinds of onigiris for 1-2 dollars! 
焼きおにぎり(Yaki-onigiri)
いりこ(Iriko)
I know this looks very weird and scary, but actually super healthy and very good for your brain and bones since it contains a lot of DHA and Calcium. Not that tasty honestly, but you can buy a full package at any grocery stores in Japan for only 1-2 dollars.
卵かけご飯(Tamago-kake-gohan)
In Japan, all eggs are perfectly safe to eat without cooking. Since they are very strictly managed and sanitized by the special law. Making Tamago-kake-gohan is super easy. By just putting a Japanese raw egg onto rice and pouring some soy sauce, you can try Tamago-kake-gohan!
In Japan, this is regarded as a super easy low-cost fast food when you don't have time (or money).
ふりかけご飯(Furikake-gohan)
A great super easy and fast meal for the time you feel super tired. All you need is just sprinkle some furikake onto rice. That's it! Enjoy!!
お茶漬け(Ocha-zuke)
Another very easy meal you can make within a few minutes especially when you don't have time and energy. All you have to do is just pouring some hot water(or green tea) onto rice with special furikake.
納豆巻き(Natto-maki)
Natto is probably the most healthy food on earth. It can help producing more hair and good skin since it has Isoflavone aka plant estrogen. However, it's not popular in the west since it's verrrry sticky and looks weird. With Natto-maki, you might be able to overcome Natto! Personally, Natto-maki is my favorite makizushi.
たい焼き(Tai-yaki)
大福(Daifuku)
いちご大福(Ichigo-daifuku)
団子(Dango)
笹団子(Sasa-dango)
ようかん(Youkan)
水ようかん(Mizu-youkan)
ぜんざい(Zenzai)
和菓子(Wagashi)
どら焼き(Dora-yaki)
今川焼き(Imagawa-yaki)
金平糖(Konpeito)
Konpeito is technically a Portuguese sweet that came to Japan around 500 years ago. With its very cool looking and awesome taste, it used to be one of the most popular sweets for shoguns back then. You could get this at any grocery stores in Japan for 1-2 dollars!
杏仁豆腐(Annin-tofu)
The white tofu-like part was originally came from China around 100 years ago, but more widely spread in Japan as a dessert rather than China today. The Japanese version comes with some fruits and kanten jelly just like the following picture.
せんべい(Senbei)
プッチンプリン(Puchin-purin)
Japanese puddings are a bit different to the western ones. Puchin-purin is more unique. Not only it tastes good but it has a special vacuum trigger at the bottom of the package to put out the pudding intact and smoothly. You can get this at any stores in Japan for only 1-3 dollars. It's worthy to try!
駄菓子(Dagashi)
Dagashi is a genre of super cheap Japanese candies and snacks mainly for kids. They don't amazingly taste great but insanely cheap! It only costs less than 300 yen in total (around 2-3 dollars) for all the snacks in the picture below. If you want to feel like a rich person, Dagashi is the way to go!