Butter a piece of parchment paper and set inside a 9×13 baking dish.
To pop popcorn on stove top, melt coconut oil in the bottom of a large heavy pot over medium heat. Add kernals into a single layer and cover with lid slightly askew to allow steam to escape. Once popcorn will begins to pop, wait a few minutes until popping decreases and then remove from heat.
Let pot cool slightly, then transfer popcorn to a bowl and set aside.
Using same heavy pot, melt butter over low heat. Add marshmallows, stir until melted, and then remove from the heat.
Add popcorn back into pot, avoiding any unpopped kernals, and mix well into the marshmallow mixture. With a silicone spatula, pour popcorn onto parchment paper and spread into baking dish.
Sprinkle popcorn with salt. Then sprinkle trail mix ingredients on top of popcorn and press down into baking dish. Let set until cool and firm, then lift parchment paper out of baking dish and cut into squares or bars.