Preheat oven to 300°F. Toast bread cubes on a large baking sheet for 20 minutes, stirring after 10 minutes. Allow to cool then transfer to a greased slow cooker.
In a medium bowl, whisk eggs and then add in half-and-half, sugars, vanilla extract, cinnamon, nutmeg, salt and bananas. Stir to combine.
Pour the custard mixture over the bread cubes, making sure cubes are mostly submerged. Allow to soak for 1 hour.
Cover and cook on low 4-5 hours or on high 2 ½ - 3 hours. It will be done when the custard is set in the center and puffy. It should not be runny, and the center temperature should be 175°F.
Allow the bread pudding to rest 15 minutes before serving. Drizzle each serving with warm caramel sauce, and a scoop of vanilla or caramel ice cream, if desired.