it might not be jeans on a formal dinner, but you do not need a tux. With a dark suit you are very well dressed on formal evenings. Sure, there are some guys that wear a tux, but I have more fingers on my two hands than men wear tux´.
Fore other evenings a lounge jacket and dark ore white trousers are very fine. For this events take a scarf with you.
Any other hints? Please ask.