Forgot to print the ticket you got from IRCTC? Not a problem, if you have a copy of the ticket in your laptop or mobile. As per the latest IRCTC notification (emphasis added) -
Electronic Reservation Slip (ERS) - The printout in standard specified Performa containing reservation particulars, and instructions for use which can be used by the passenger along with the relevant authorized Identification, as travel authority for performing the journey.
Virtual Reservation Message (VRM) - A screen-shot of the e-ticket displayed through laptops/palmtops/ Mobile phone is referred as Virtual Reservation Message (VRM).
ERS/VRM along with any one of the eight prescribed ID proofs in original and the indication of the passenger(s)' name(s) in the Reservation Chart will authorize the passenger to travel.
VRM combined with valid photo-id in original will be treated as an instrument on par with the ERS.
ERS/VRM along with one of the eight prescribed proofs of identity in original will also authorize the passenger to enter the platform on the day of journey and he/she will not be required to purchase platform ticket. ERS/VRM along with original id proof will be required to be produced on demand of Ticket Checking Staff on the platform.
-- as per https://www.irctc.co.in/VRM.htm
What this means is that you can show a screenshot or pdf of the ticket from IRCTC along with your ID card in original (which you needed to anyway) instead of a printout.
Save paper, save trees. What an idea, sirjee :)