Cooked vegetables - Sauteed or roasted onion, pepper, eggplant, or even zucchini. This is a great way to use up leftovers.
Meat - Bacon is a no-brainer, but salmon or lox is fantastic too. I've also tried (and loved) thinly sliced steak. Another great way to make a dent in your leftovers.
Seasonings - Salt and pepper are a must. But definitely mix things up sometimes with garlic, paprika, , and everything bagel seasoning!