I left my bag in the overhead compartment.
di-men-ti-CA-to — stress on fourth syllable. 'Vano' is VA-no.
After disembarking or just before leaving when you realise you left something in the overhead bin.
'Ho dimenticato' (I forgot/left behind) is the passato prossimo of 'dimenticare'. 'Nel vano portabagagli' (in the overhead compartment) is the precise location. Report immediately after disembarking — cleaning crews find items and hand them to lost property, but recovery is not guaranteed.
Ho lasciato il cappotto sopra.
I left my coat up there.
Can go back if you haven't left the gate area yet
Mi sono dimenticato le cuffie sul sedile.
I forgot my headphones on the seat.
Report to the airline desk immediately
Ho perso il passaporto a bordo.
I lost my passport on board.
Emergency — contact airline staff and then the police
Items left on aircraft in Italy are handed to the airline's ground staff, who send them to the central lost property office. Recovery depends on how quickly you report the loss. Travel insurance may cover the cost of replacing items if not recovered. Always do a final check of your seat, seatback pocket, and overhead bin before deplaning.