A method includes: a travel planning system, via a user interface, receives requirements for a trip from a user; collects preference information of the user for the trip; searches available travel options based on the requirements and the preference information; builds an itinerary based on the searched travel options by use of a balance combination of relative weights for sources of the preference information; applies external data relevant to the itinerary; obtains a response to the itinerary from the user; either adjusts the itinerary or makes reservations respective to the travel options in the itinerary, depending on types of a response from the user; records at least one change to the itinerary via the user interface in a user device while the user device is off-line; and responsive to the user device getting online, synchronizes the at least one change to the itinerary stored in the travel planning system.