Another version we had was with pesto and some leftover grilled vegetables (zucchini, onions, red peppers.) They were amazing.
For the kids I use the same bread, spread it with a little (usually leftover) spaghetti sauce, add some fresh mozzarella and call them “pizza paninis.” They love them.
P.S. I love my panini press. It is one of my most-used kitchen tools in the summer.