When you’re flying in the ‘back of the bus’ you don’t get a lot of person space. Airline coach seats are small. You get the space underneath the seat in front of you for your feet. And there are overhead bins.
Traditionally, you can bring a carry on bag on board and a personal item. That carry on goes in the overhead bin, and the personal item like purse or laptop bag goes by your feet. But these are social norms, not rules. Some passengers are going to put their personal item up in the bin, too. What do you think about that?