Preheat the oven to 250F° and position racks in the upper and middle thirds.
Toss the popcorn with the roasted peanuts in a large heatproof bowl.
In a large saucepan, combine the brown sugar with the butter, agave nectar, corn syrup and salt and bring to a boil, stirring until the sugar is completely dissolved.
Boil over moderate heat for 4 minutes.
Remove from the heat.
Using a long spoon, stir in the baking soda and tequila; the syrup will foam. (See Note 4)
Immediately pour the hot syrup over the popcorn and peanuts and, using 2 spoons, toss to coat thoroughly.
Spread the popcorn on 2 nonstick baking sheets and bake for about 1 hour, stirring occasionally and switching the sheets halfway through, until golden and nearly dry.
Turn off the oven, open the oven door completely and let the popcorn cool completely before serving.