My most valuable was probably a copy of Chrono Trigger for the SNES but I sold it in like 2000 for a copy of WU Tang Clan, Roll Cage, and some other PS1 game that I can't even remember.
Also traded in a copy of PS2 Disgaea and Vandal Hearts for a DS Lite and Wii horizontal stand.
Currently, I guess Gravity Rush Remastered is the only game I own worth a little. I lucked out and bought it on day one because I loved the series.
Lost my SNES copy of Chrono Trigger in a bad break up...
*sad music plays*