So many. Everything I love goes away. The first that comes to mind is Crescent brand au jus. It was the best out there, period.
The next is the bruschetta chicken ciabatta sandwich that Jack in the Box used to have. Amazing.
Uno candy bars are technically still around but impossible to find. I love those little bastards.
There are more but I can't think of them. Do the myriad of products that changed their recipes thinking no one would notice count? I noticed. Sometimes the new thing is dead to me.
Also those old "fire" "rain" element drinks (sobe?) were unbelievably good. In fact sobe was so good in the 90s/00s but changed recipes and packaging so that stuff is bleh to me now.
Original Surge cola. They changed it for the relaunch and it never was quite right. I used to have one every day before [sport] practice in high school.
Oh! Trader Joe's had this pepperjack quiche that was out of this world. Haven't seen it in years. It was the only reason for me to go there.
Edit: this post made me hungry and sad