I love this idea. It's simple, effective, and the UI is great. The account creation process is such a relief. Editing and saving trips is delightfully fast. A few suggestions:
* When adding an activity (or route), I instinctively look for a button at the buttom that says "Save activity". And possibly one that says "Cancel". Right now it's immediately saved and appears on the itinerary. That might be faster, but it leaves me feeling anxious about state.
* The ability to share a Trip with others and even to allow collaboration would be a game-changer. Might require you to allow people to view/create/edit Trips with a "guest" account.
* It would be amazing if there was a way to automatically generate driving or public transport directions and have the Activity and Route both added into the itinerary.