I always keep my reg, dive computer and log book/c-cards in my carry on(and maybe your mask). I have never had any problems. Recently, one TSA agent opened the bag and wanted to know what it was. Then right away another agent came running over, explained what it was to her and quickly gave me the bag back and he actually said "sorry about that".

I have found most TSA agents have been very polite and nice. I suppose they must have some training as they are dealing with tricky situations all of the time.