Any time I travel I inevitably end up accumulating a bunch of small change, and it always begs the question of "what should I do with it?". Sure, you can buy a bottle of water at a convenience store or vending machine, or maybe a few snacks, but if you want quirky souvenir-style items, Japan has you covered. Gachapon machines (also sometimes written as gashapon) are perfect for using up those coins and having something fun to remember your travels with.
Most gachapon machine items are priced at around 200 to 500 yen, and the price varies depending on the "prize" you might get inside. The term gachapon is actually an onomatopoeia, where the "gacha" sound is the turning of the crank to release the prize, and the "pon" is when it drops into the chute below. The gachapon prizes can be anything from small key chains to costume jewelry items, little plush toys, and more. Basically, if it can fit into a a plastic gachapon egg, it's fair game! I've seen plenty of fun things on offer, from rings that looked like chocolate box pieces, to Anpanman and Pokemon toys, mini makeup mirrors, and even band merchandise. You'll usually find a bunch of machines located next to each other, so it's easy to pick one (or several) that you'd like to try your luck at.
As for where you can find gachapon machines, the real question might be "where can't you find them?". They're all over Japan, from large shopping malls to game arcades, and often inside transportation hubs like airports and train stations. As well as helping to get rid of the coins you may not be able to use before departing Japan, gachapon toys are a fun keepsake either for yourself, or for your friends and family members!
Over the years I've got a few interesting ones, like a mini-Gameboy that actually works, a shamisen that's put together exactly like the real thing, and a small lantern with Hikonyan that's better than any other souvenir I could find in Hikone.
As for the stuff inside, the Kaiyodo Figure Museum in Nagahama (http://www.ryuyukan.net/) not only has lots offer bigger figures, but also thousands of those small pieces of art found in those eggs. Well worth a visit!