We went with Chucky and Sumita and we packed snacks (chesses, crackers, chips, and brownies) and ordered a mushroom and pepperoni pizza ($13) from a nearby restaurant, Eileen's. It's located on Merrimack St, just a short walk from the concert site.
I was pleasantly surprised by the pizza – the mushrooms were fresh, not canned (although they were not sliced, but hacked up in uneven chunks). The crust was decent, although it could have used another 3 minutes in a pizza oven. Given our limited options, it was a fine dinner choice.