There are left luggage lockers (which include plugs where you can charge phones and such like) at Gara de Nord in the First Class ticket office. They cost from 5 lei (for three hours) to 10 lei (for ten hours). There is also a conventional left luggage service close at the station, close to the main exit, where it costs 5 lei per small bag per 24 hours. You will need ID. There are no left luggage facilities at the airport.