Two people is the usual number for a standard field crew for a simple monitoring-type job; you're not out in the woods totally alone, and two people can fit safely into one cargo van or pickup truck. We always met for dinner at night, unless we were lucky enough to have a kitchenette and a per-diem job. In that case, we disappeared into our respective hotel rooms to cook pasta or grilled cheese sandwiches or something.
So I spent a lot of time going out to dinner with one male coworker. Restaurants see this and they think "date", unless the coworker is 10-15 year older. In that case I always felt sort of awkward because I felt like other people were thinking "he's way too old for her" (remember, I look 10 years younger than I am). This leads to sort of funny situations where we're given some romantic booth in the back corner.
I've had dinner with lots of folks over the years, and only once has the meal ever been awkward because my male tablemate tried to pursue some sort of romance. In that case, I think the person I was eating with would have made a pass at any female who made the mistake of straying into his orbit. He was the only person who I actively hid my hotel room from as well, incidentally, because he completely creeped me out. It did make me appreciate the scores of normal, professional dinners I had with all the other guys I've traveled with.