Planning to Make Unplanned Purchases? The Role of In-Store Slack in Budget Deviation

We propose that consumers have mental budgets for grocery trips that are typically composed of both an itemized portion and in-store slack. We conceptualize the itemized portion as the amount that the consumer has allocated to spend on items planned to the brand or product level and the in-store slack as the portion of the mental budget that is not assigned to be spent on any particular product but remains available for in-store decisions. Using a secondary data set and a field study, we find incidence of in-store slack. Moreover, we find support for our framework predicting that the relationship between in-store slack and budget deviation (the amount by which actual spending deviates from the mental trip budget) depends on factors related to desire and willpower.