Impulse buys may not be a matter of impulse says a new study in the Journal of Consumer Research. Shoppers often expect to buy a certain number of “unplanned” items, the research found, and most have a mental budget to accommodate those buys. The study calls this concept “in-store slack.” Consumers indicated that they employ the strategy because they anticipate forgotten needs and also because they know they’ll encounter “unplanned wants.” (Planning to Make Unplanned Purchases? The role of in-store slack in budget deviation, Journal of Consumer Research : August 2010,