What is your favorite type of project to take along on holiday/vacation?
All of them? I usually pack for project with the idea that if I lost on a desert (or not so desert) island, all the survivors will have sweaters, and socks, and blankets.
For my long flights to Italy, I bring a sock project to knit on the plane. I can tell you exactly how much time I need to knit a sock: SF to Amsterdam. One sock going, second sock when I come back.