More and more transit agencies in the Bay Area are steering away from paper day passes. Even MUNI is ridding their paper transfers sometime next year, and VTA is joining the group.
On the turn of next year, January 1st, 2016, VTA will no longer issue or accept the good-old Day Pass. For all of those currently weeping, the Day Pass isn't going away completely - you can exchange any leftover Day Passes for Day Pass tokens distributed from public and social service agencies.
The best way to pay your fare in 2016 is with a Clipper card, but you can also still pay with exact cash fare on VTA buses and you can still purchase one-way tickets at VTA Light Rail ticket machines.