〜ないと: if you don't; have to (casual)

Casual form meaning "if I do not", used to mean you must do something.

Verb negative + と, usually with いけない dropped: 行かないと. As a full sentence it means a strong obligation. Also negative if-clause: 急がないと遅れるよ. Casual speech; in formal use 〜なければなりません.