advantage of our environment. probably just like we did thousands of years ago. >> reporter: so conditioned, in fact, that most of us, without knowing it, budget up to one-third of our grocery money on impulse buys. >> do you have any idea of a rough ballpark of how much money you're going to spend? >> under $150. >> it will probably be over $200. >> reporter: what about all of this? >> so not on the list. >> reporter: shelley and rachel both bought a table full of treats they hadn't planned on. still, shelley spent what she predicted. and rachel, even with her pie and oreos, spent less. >> what it says to me is shoppers are smarter than even they think. >> reporter: even when they're not thinking about it. barbara pinto, abc news, westport, connecticut. when we come back this morning, the year in review here at "world news now." >> the highs and the many lows of our performances in 2010. you don't want to miss it. wswsw4