。
I forgot to bring my insurance card.
Literal
Insurance-card [obj-を] take-and-come [nominalizer-のを] forgot-(regret) (polite).
持って来る is a compound verb (持つ + 来る) meaning 'bring (here)' — literally 'having it, come.' Paired with ~てしまう, the forgetting carries regret. のを忘れる is the nominalized-verb-object construction for 'forget to X.' A compact sentence that's actually dense with structure.