Japanese fuku (福, good fortune/luck) and fukuro (袋, bag). = Fukubukuro
Fukubukuro is used to refer to the 'lucky dip' sale bags that a lot of Japanese stores release on New Years day. The bags aren't just for clothes, they can also be for food, cosmetics, electronics and well pretty much anything!
They generally cost around 1,000 yen to 10,000 and have any number of items in them with the goods being valued up to 10,000 yen, some stores even produce special bags/suitcases for their Fukubukuro. They are like a luck dip because you don't know what items are inside each bag or the value, but that's half the fun
It is well worth a look at if you are in Japan around new years.
The fuku comes from the Japanese saying that "there is fortune in leftovers" (残り物には福がある). Popular stores' fukubukuro usually are snapped up quickly, Shibuya 109 in Tokyo will have a line wrapping around the block with customers eagerly awaiting the New years sales.
You will often see people set up a make shift swap shop outside large stores, to swap the contents of their Fukubukuros.
More Fukubukuro's below