Fulfilling goals in open-ended tasks like grocery shopping requires sequential navigation of countless options. When deciding what to choose next, we propose that past choices cue retrieval of subsequent options from memory. Moreover, each past choice may function as a cue to multiple knowledge sources, such as episodic, semantic, and hierarchical relationships involving the item. We evaluate this account of open-ended sequential choice on the purchase sequences of over 100,000 online grocery shoppers. Consistent with our account, we find that consumer choices are predicted by their similarity with their previous choice, suggesting that past choices cue retrieval of subsequent options. Products that co-occurred in the same episode, were nearby in semantic space, or neighbours in a semantic hierarchy were most likely to be chosen, suggesting that consumers queried multiple types of long-term knowledge. We evaluated a wide array of formal models and found that the one that best accounted for people's choices included retrieval cues for all three knowledge types. Models fits to individuals allowed us to assess how much they relied upon each knowledge type. The type of knowledge that people most relied upon determined the type of errors they made; more episodic retrievals predicted fewer forgotten items and more semantic retrievals predicted more items being added to one's basket that they didn't otherwise need. Our results demonstrate how basic retrieval mechanisms shape sequential choices in real-world, goal-directed tasks.