hold on to sth | ˌhold ˈonto sth
1.
to keep sth that is an advantage for you; to not give or sell sth to sb else :
You should hold on to your oil shares.
She took an early lead in the race and held onto it for nine laps.
2.
to keep sth for sb else or for longer than usual :
I'll hold onto your mail for you until you get back.