You're going to need something to write your lesson plans in, right? Even more than convenience stores, ¥100 shops are your best bet for cheap notebooks. Color coding them can also help you keep track of different classes or different schools.
11. Origami Paper
Teaching colors? Origami paper is the easiest way to go. If you get a good set, you might even find metallic silver and gold, which are great for getting kids' attention. Just be careful when they try to take the shiny ones for themselves!
Stickers can make for great in-class prizes—just be aware that once you start giving them out, you'll have to have enough for everyone! However, ¥100 shops will have a huge array of stickers to choose from, and you can get plenty on a single sheet.
If you need "big" gifts for key events like kids' birthdays, ¥100 shops will also have cute erasers that can serve fairly well without engendering too much resentment from kids who don't get one—but again, they'll all expect one eventually, so be careful of the precedents you set with presents!
Balloons are great, simple tools that can be used for drawing faces or passing around the class in a relay. Latex allergies are essentially unknown in Japan, so they can usually be given to kids without any trouble—except, of course, that they'll all want to play with them!
8. Egg Timers
It's usually a bad idea to use your cell phone in class—the teachers spend all day trying to make sure the kids put them away, so it looks pretty bad if the ALT pulls one out. Most schools will have stopwatches for gym class, which you can use in a pinch. However, nothing beats the total randomness and anticipation of a cheap egg timer!
7. Seasonal Stuff
¥100 shops are you absolute best bet for seasonal decorations and knickknacks. Halloween and Christmas are the two biggies, and you'll find no shortage of Jack-o-lanterns, creepy-crawlies, Santa hats and stockings well before the time comes.
6. Dice & Cards
These are great tools for in-class games and for randomly selecting student volunteers. If you're lucky, you might be able to find a set of dice and cards combined.
While most classrooms will have magnets, there never seem to be enough for all the flashcards and visual resources needed for an English lesson. So it's always best to come equipped with your own set. Don't bother with the little ones—they can't hold a blessed thing. Unless you want to be catching falling papers all day, be sure to go big!
4. Carrying Box
If you're carrying a bunch of magnets, dice and playing cards (and it's good to have them all on hand in a pinch!), you're going to want a box to put them in. Just make sure it has a good latch! This box is going to get knocked onto the floor at least once a week, and you don't want the contents spilling everywhere!
3. Magnetic Tape
Not every ¥100 shop will have this, but if you can get your hands on it, magnetic tape lets you take your flashcards to the next level. Simply cut the tape, apply strips to the backs of your flashcards, and boom—no more fumbling with magnets!
The only trick is that the magnetic tape can be rather weak, so make sure you've got enough to hold things in place. Another worry is that it can get both time-consuming and costly to prepare every single flashcard with some of this tape. But that brings us to our next level-up item...
2. Hard Card Cases
These can be found in a number of sizes, but B4 is likely best for classroom purposes. You'll have to invest in about a dozen of these to start, but after that, your flashcards will be both invincible and interchangeable. Just slip one flashcard into each case and you're done!
Of course, the cases are typically too heavy to work with anything but the strongest magnet, which is where your magnetic tape comes into play. Apply a few strips to the back, check that it holds (and check the weight with paper inside!), and you'll never have to worry about flashcards again! It's satisfying to simply hover a flashcard over the board and get it to stick—sometimes you can even get a gasp of appreciation out of your kids!
Being an ALT means having lots of resources, and you're going to need a place to keep them. Clear files are a great way to keep yourself organized. You're also going to need some kind of folder for carrying your flashcards to the classroom and introducing them to your students in an enticing way. It's much more fun to build anticipation by slowly pulling your next image out of a brightly-colored folder than to simply hold it up and say, "Dog." Make your folder part of the fun!
Make sure your flashcards are arranged in order in your folder so they essentially prompt you through your lesson. This will keep you from having to check your lesson notes and make your teaching look effortless. A well-prepared folder can be the key to a successful lesson!