Whole wheat bread sandwiches with peanut butter, ham, and spinach. Even ignoring the "no bad effects" condition, I'd still go with it. Good balance of carbohydrates (bread), protein (ham), and fat (peanut butter), with some spinach for added benefits, and taste. And it's friggin' delicious.
Whoever came up with the idea of combining different foods together between two pieces of bread should have a holiday named after them.