Background: Packing fruit, vegetables and whole grains in preschool children's sack lunches is a powerful way for parents to teach their children eating habits and food preferences to support a lifetime of good health. A multilevel intervention pilot-tested in childcare settings increased servings of vegetables and whole grains, but the lunches still fell short of the intervention goals. Purpose: Secondary analyses were conducted to identify specific behavior changes underlying achieved increases in servings of vegetables and whole grains. Methods: Food records from direct observation of 769 parent-packed lunches were investigated to unbundle and measure multiple aspects of lunch packing behavior. Changes from baseline to six week follow-up for the intervention (N = 81) and comparison (N = 51) parent-child dyads were evaluated in multilevel modeling. Results: The increase for whole grains was explained by more parents packing whole grain items whereas increase for vegetables was explained by parents packing vegetables on more days. Discussion: Tailored options were identified for further strategies to increase vegetables and whole grains in parent-packed sack lunches. Translation to Health Education Practice: Linking achieved outcomes to specific behaviors can be an aid in assessing needs and designing interventions to maximize the chances for success. (Contains 2 tables.)