Kopytka are usually served with thick sauce, which often adds dominant flavour to the dish. Wild mushroom sauce is probably the most popular option (porcini being often substituted with button mushrooms for economic reasons). Famous Polish milky bars inevitably have 'kopytka w sosie grzybowym', kopytka in mushroom sauce, on the menu, at least the ones I used to frequent always had.
For this particular batch I used instant sauce, because it's, well, instant. It was delicious, with velvet-like texture and strong flavour, but it was also full of nasty chemicals the names of which do not ring a bell with anyone without a Ph.D. in chemistry. I usually make my own sauce - my Dad, an avid (and certified!) mushroom-picker supplies me with industrial quantities of dried porcini so I never lack ingredients. I have some extra for sale if you were interested :).
You can always use cheaper mushrooms - there's nothing like the real thing, but button mushrooms are an acceptable substitute.
Italians serve their gnocchi with tomato sauce. I'm not used to such a combination so I cannot honestly recommend it, but I guess it's worth a try.
If you want to keep things simple, you can forgo the sauce altogether and serve your kopytka with melted butter, fried breadcrumbs, fried onion or bacon.
Kopytka taste just as delicious (perhaps even better) on the next day, re-heated on the frying pan with some butter. Just fry them until golden and crunchy. I would illustrate with a picture, but my kopytka have already disappeared :)