Are you asking just about
Disneyland or are you interested in DCA as well?
Several seats by Harbour Galley are currently not available. They are cordoned off for Tiana related construction. Tiana's opens on Nov 15, so if your trip is after that, they might be available.
Right now Edelweiss Snacks sells the garlic cheese bread with brat. It is a very popular item, so the Motor Boat Cruise dock is filling up faster than it used to. Still, if you can find a table there, it is a nice spot. I was walking by last week and saw the Mad Hatter, Alice and Peter Pan having a tea party. This was around 10:20 am and you can see that tables were still available.
Are you looking for a view or to get away from crowds? The outdoor dining area at Alien Pizza Planet is often more calm, but doesn't have a view. Similarly, Craftsman Grill (QS) or Craftsman Bar (table service) in the GCH are a little calmer. The top of Hungry Bear can be calm and has a view of ROA. However, it is currently being refurbished and, when it opens, it will have a new menu so will likely be crowded.
Edit to add: There are tables on the east side of Tom Sawyer's Island (facing the Mark Twain dock). If you don't mind carrying your food out there, it is a really nice, calm and scenic place to eat.