If you live in Japan, you probably won't have many visitors. Family visits are common enough, but most Japanese houses are too small for gatherings. That explains the popularity of coffee shops, restaurants, karaoke places, izakayas (Japanese pubs), and the massive gatherings of high school kids at local family restaurants in the afternoons.
But if you do have casual visitors over, you'll probably offer them some tea and a simple snack. You can offer senbei, which is a flat rice cracker that's grilled and usually covered with soy sauce. Or you could offer a similar snack called okaki.
Okaki is fried and is more three-dimensional. It also seems to come more commonly in variety packages to mix up the flavors - there are different seasonings and styles.
The above bag was under 200 yen (less than $2) and has a lot of different flavors. They're all pretty good, and it's a nice snack to have with beer in the evening. Expect a somewhat salty savory snack; they're crunchy but usually not too hard. Perhaps if you visit my tiny apartment I'll share some with you too!
There are many other Japanese crackers that I haven't even tried yet... yet!
Japan has a very big potato chip market, which I think are much more popular as daily casual snacks at home, with lots of great limited flavors. But oddly enough corn chips have never really taken off here, though Doritos has really been pushing their "Gourmet" line lately with what seems to be a new flavor on shelves every week, lasting for about a week before the next taste arrives.
So, what do you serve guests at your house?