One option is to use different kinds of cheese. my favorite is a slice of Velveeta with a slice of provolone. Velveeta and pepper jack is good too. Another option is to add some kick by spreading some sriracha or barbecue sauce inside before cooking.
Adding meat is another way to kick up your grilled sandwich. A bit of pepperoni, a slice of ham or a slice of salami makes for a great sandwich.
Some people like using mayonnaise instead of butter or margarine to give the sandwich a better taste, but I’ve had it that way and didn’t like it at all. I’m not a fan of miracle whip either.
Oh, and if you’re looking to get some veggies in without noticing it (especially for the kids) super finely mince carrot or broccoli and put it in, or thinly slice tomato and put that inside the sandwich.
Image: Public Domain, Morguefile