I haven't lost a customer service fight in seven months

It started with a box of Annie's mac and cheese. Three boxes, actually, a Costco three-pack, and not one of them had a cheese packet. The kitchen is chaos because kids are hungry, and I'm standing there looking at the box of dry pasta thinking about what a consumer is supposed to do here. Go back to Costco, stand in line, (wait... did you remember to bring the box?) - for six dollars? Write to Annie's? I'm not writing to Annie's. Every version of "do something about it" costs me more than the problem.