must ... in advanceUsually appears as ～ておかないといけない or ～ておかないと, meaning that something must be done beforehand or kept in a certain state. The ～ないと part literally means “if not,” but the full expression means “must” or “have to.”
must ... (or else)Usually follows a て-form as 〜ておかないと, meaning that something must be done beforehand or kept in a certain state; 〜ないと literally means “if [you] don’t ...” and often implies a negative consequence. The subject is often omitted.