Preheat oven to 400°. Line a cookie sheet with parchment paper. Place saltine crackers side by side until the sheet is filled. Set aside. In a saucepan, melt butter and dark brown sugar.
Remove from oven and evenly distribute chocolate chips onto the boiling caramel. Add in the Reese's Pieces, any other candies, and pecans. Spread with a spatula if needed. Put cookie sheet back in oven and let cook just long enough for candies and chocolate to melt.
Once melted, remove cookie sheet from oven and place in the refrigerator to chill for 1-2 hours. Once bark is cold, remove from fridge and break bark into bite sized pieces. Store the candy bark in the refrigerator or in an airtight container for up to 2 weeks.