If you're coming from Pune/Lonavla on Sundays after some sightseeing/fun trips & see that Pune Mumbai Intercity Express is fully packed, then need not to worry. You just purchase a General Unreserved Ticket & board this train, as this train's Unreserved coaches are almost empty, plus if your destination is in Navi Mumbai or in Western suburbs of Mumbai then just alight at Panvel/Vasai.Rd.
Try to board the General coaches which are in front side just after Engine & SLR, you can then happily enjoy your trip.