If they want to put the cake in the overhead bin don't they have the right to. I myself always follow the direction given to me by crew members. I have a small carry on bag on many trips and often I am asked to take it from the bin if room is needed for larger bags and move it under the seat in front of me. This causes me issues sometimes as I like the area there clear for my feet. Don't I have the right to keep the small bag in the overhead bin. If there is not enough room for larger bags they should be checked in. If there is a shortage of space airlines don't charge you to check a bag.