That is the problem of having a non proactive flight crew (or them just being so busy that they arent keeping up with things). If you are boarding the back and the rear FA can see that happening, they should make an announcement that you need to bring your things back with you. I've seen some crews stationed at the exit row mid cabin to assist with this and others just hang out at the front. What is the procedure when boarding? I know A at the front and one in the back, but what about the 3rd?