I see this used but I can't figure out what it means.
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Please add more context. Where do you see it used and by who? – Earthliŋ♦ Jul 18 '16 at 5:56
かこっかな is a more casual way of かこうかな(書こうかな), and 〜うかな means "I'm wondering if I should 〜." So the phrase means "I'm wondering if I should write something". I don't know the whole sentence but かこっかな means this.