I have no addons, I see FP markers. And sometimes golden Quest helper arrows as well
And yes on the crate you could mount 
But you were dismounted when getting on or off the boat.
Carets fill up my minimap - they have been reason for me to get killed more than once 
I forgot a lot of things, but those three, I know were not in Classic / TBC
I forgot stop on request arrow (which I never use, but still relog) “Open all mail button”, send stacked items, map not closing open bags upon opening and surely a lot more.
And of course none of these as such ruin my gameplay, they just break immersion. They are a part of why I do not play as much as I would really like.