Trimet, CTRAN, and Portland Streetcar are transitioning from paper tickets and tickets via apps to an electronic ticketing system called Hop Fastpass.
They are hosting one final in-person ticket swap event on Saturday, 12/14, at Pioneer Courthouse Square from 9 am-1 pm. If you swap remaining tickets (paper or app), Tri-Met will give you a Hop Fastpass ($3 value) loaded with the equivalent value.
Hop cards are available at retailers like supermarkets, pharmacies, and convenience stores and do not require the use of a smartphone, though there is an app you can use for convenience.