Start by popping your popcorn if you're making it from scratch, then pick through it and remove any unpopped kernels. You want a clean base with nothing hard hiding in the mix. Let it cool slightly before moving to the next step.
While your popcorn cools, slice your crispy rice treat bars into small, bite-sized squares. Keeping the pieces small makes the mix easier to scoop and share, especially for little hands grabbing a handful.
Add your popcorn, pretzel sticks, candy-coated chocolates, crispy rice squares, candy corn, and rainbow chocolate chips into one large mixing bowl. Add everything gradually rather than all at once, which keeps the mix from clumping unevenly.
Using a wooden spoon or your hands, gently toss everything together until each ingredient is evenly distributed. Be gentle here, since tossing too roughly can crush your popcorn and crispy rice pieces.
Once everything is mixed, scoop portions into individual treat bags, cups, or a big festive bowl for sharing. This mix is ready to eat the second it's combined, so there's no waiting around before serving it up.