I commute a lot on coach buses and often have my bag on my lap when bus is full.
However, there are bars in front of, or next to, seats.
I can just hook may backpack and make it easy to access my bag's contents. It sort of becomes a shelf.
I provide two versions. The lighter version is fine for a simple backpack with a laptop and a few devices or books. It will break if someone pulls down on it hard.
The Dilophosaurus version is extra strong - no failures yet. The Dilophosaurus has a recess in the hook to glue an inner tube or some other rubber/leather to increase grip on bars. This prevents your bag sliding when the coach/bus turns sharply.
The author marked this model as their own original creation.