PAN Card, Voter ID etc. Because you must provide a valid ID Proof in order to book a tatkal ticket and even make sure you maintain that valid ID Proof with you on data of journey. You may be asked for verification.
but sometimes are unable to plan, so one needs to book tickets in Tatkal on IRCTC website.Tatkal means quick, but booking Tatkal ticket online on IRCTC website is anything but Tatkal(quick)