Another one I've noticed is using "I've" as a contraction in e.g. "I've a meeting to attend". Seems totally reasonable but for some reason native speakers just don't use it that way.
As in “I’ve done it” or “I’ve seen it”
It would not be used before a noun, in the context of ownership, as in “I have a meeting”
Even just reading "I've a train to catch" gives a British accent in my mind.