Heaps of great suggestions here already... Thai chicken patties are simple to make, with a sweet chilli dipping sauce. Chicken / mayo / chive sandwiches on white bread are always pretty popular! simple pizzas made with circles of puff pastry, tomato paste, cheese and a couple of simple toppings... lamb meat balls with relish...

And mini cupcakes, just simple ones with plain icing, always seem to get eaten!