The elites always get to go on with the pre boards but if you are a little late just go, they won't stop you whenever you get on. And yes I almost had a problem when I flew with a companion that doesnt have elite. I waited and then got on and saw nearly full bins. I was able to move a small bag around to fit my carry on but it was close. I don't know what they would do, maybe they would find space in the bins saved for the first row, but to be safe just get on earlier if you have elite.