I am bad at fashion. Help me! I need a dress to wear to my SIL's wedding in October. The dresses I have worn to other weddings I've attended are too summery (plus, they've been in a million photos already).

Relevant facts:

1. The wedding is in late October in Minnesota, so it may be chilly.

2. The wedding is on a boat.

3. After the wedding, we are going on a party bus to go bar hopping. (I am really not excited about this part).

So I'm looking for something fancy enough for a wedding, but not so fancy that I feel weird when wearing it bar hopping later. I pretty much never wear heels, so I'll probably want to wear flats (or boots?). I like wearing black, but am open to colors. Nothing too bright though! Any ideas?