Do you do the same in the car? The times I'm most inconsistent is in the car. Mostly she is upset because she has either dropped something like a book or soft toy that she wants or is just plain bored of sitting there. Sometimes I try and distract by talking to her about something else, sometimes I try and reach something else to give to her or other times I ignore her, after first telling her I'm busy and can't help her right now.
Anyway, it's not working because even a 5 minute journey ends with her whining!
Sometimes I feel like I need one of these...