Well based on this past summer and I don't know if any of these will be open when you go to P'Town but:

Agree about Ross' - not the cheapest, but not the most expensive either.

Of course if pushing the boat out - Chesters (fab). Also in the pricier category is the Red Inn as well (don't know your budget, but worth checking out. Pretty reasonable for lunches).

Don't know if it will be open, but Devon's was great this past summer. It was the Little Fluke (which has moved to Truro. Not recommened by the chaps we stayed with this summer, BTW). Devon, who did the brunch/lunch at Little Fluke has taken over the evenings as well and does a nice job.

We ate at Martin House last year and it was nice. We were advised that it's gone down hill a bit. Our hosts ate there this past summer and were not impressed at all.

Lorraines was pretty good for Mexican. And IIRC not too badly priced.

Again, not sure about this time of year, but you could always go stock up on nibbly foods from my fave - Relish! They may even put together some platters for you if you don't want to eat out. For lunches, we absolutely loved this place - really nice sarnies! ^ ^