noun
lucky bag; mystery bag; grab bag
A sealed bag sold at a set price, especially during New Year sales, containing a random assortment of goods whose total value is usually higher than the purchase price.
元旦にデパートで福袋を買うのが毎年の楽しみです。
Buying a lucky bag at the department store on New Year's Day is an annual pleasure.
この福袋に
You won't know what's inside this mystery bag until you open it.