Pinkie Pie has seen Twilight frown and wander the edges of town, looking into the horizon. She knows what troubles her immortal friend. Her life is short after all, at least compared to that of an alicorn. It stings her heart to see a friend so sad.
So, she prepares a gift for Twilight. It might not be much, but a single memory might weather the road ahead.
This is that memory.