Just a quick something I came across, can't see any posts saying the same, correct/flame me if I'm wrong.
Stacking the buff food correctly can increase the duration - for example, if you have 15 Toasted Smores with 7 days left on each, and 5 Toasted Smores with 14 days left, by dragging the stack of 15 onto the stack of 5, you get a full stack of 20 that all have 14 days left, enabling you to buy some on the last day (As I imagine most people were planning to) And upgrade your old stuff to get the maximum time from that.
Be aware this works the other way around, so stacking incorrectly can shorten the life of that buff food.