Here are some things I do ahead for impromptu visits
We have a great Chinese restaurant in town and I always order a large container of chicken fingers and another of wings, then freeze them. If someone stops by, they reheat beautifully on a pre-heated pizza stone. I always have sauces on hand.
Also, shumai and gyoza dumplings freeze well & you just pop them into boiling water & serve with a simple dipping sauce.
I've reheated BBQ ribs after freezing them. Just slop on some xtra bbq sauce after heating. A pizza stone is great to have for all kinds of reheating.
Another thing I do ahead are chicken tacos. Just saute shredded chicken in taco sauce (I add peppers & onions or whatever), let cool, then roll in soft taco shells, wrap individually and freeze. You can warm them in the oven or put a bunch in a casserole dish, throw some salsa & cheese over them and heat. Serve with sour cream, guacamole, black olives, etc.
I could go on and on. Fried ravioli are easy; pierogi, aloo gobi pastries.