I like the idea of serving something less-than-substantial, and not too costly.
Boiled eggs and toast, or tuna sandwiches. Or keep a carcass from a chicken and make broth with it, then throw in some chopped vegetables (1 carrot, 1 onion, 1 potato and 1 stick of celery - kind of wilted if you have it on hand). Don't add leftover meat or noodles or rice, just broth and veggies.
Apologize profusely and say that you didn't have time to make a big meal / didn't get to the supermarket / have had to cut back your grocery budget but enjoy their company anyway. Or you could comment on how you've been researching dietary habits and are trying to get back to basics.
