Westerners are no strangers to the concept of souvenirs. We bring back little presents, knickknacks, or snacks to our close friends and relatives when we go somewhere far away, and generally expect the same.
In Japan, this concept is far more significant and (as expected) much more comprehensive. Many people already have an idea of Japanese お土産 (omiyage), but might not realize how integrated into the culture it is.
Put simply, when you travel somewhere, you’re expected to buy お土産 for not only friends and family, but your coworkers. This applies not just for vacations, but also weekends away and even business trips. If you go to different places, you’re expected to get stuff from each place as well. Generally, obligatory お土産 takes the form of individually-wrapped snack food common to the area(s) you visited, and is usually bought in handsome packaging at shops in the train station or airport at inflated prices. As you might guess, frequent travelers can end up spending a lot on overpriced snacks for people they may not even really like.
I’m not going to say I don’t participate in this cultural tradition, but I try to do it smart: rather than buying at the overpriced stores, I look for a ドン・キホーテ (Don Quijote), a chain known for carrying basically everything you might need and vast amounts more that you don’t. They have plenty of お土産 for purchase, and at much more reasonable prices.