Those are good suggestions from Finlero.
While Newbury St is fun and fashionable, most of the food choices are not that great. Instead, look into places on Boylston. There are lots of places on the blocks west of Dartmouth St that are quite good. I like Sel de la Terre. Also there are Bangkok Blue and Chilli Duck for Thai, Abe & Louie's and Mortons for steak, Atlantic Fish for seafood, McGreevy's and Lir for pub food, and for high end L'Espalier. All would be good and many have outdoor seating.
Hi and welcome.
You'd definitely do well to do search the board so you can get some better-tailored recommendations, or at least give us some specifics as to what you like so we can be more helpful, but in the meantime, out of thin air:
Snack near Boston Common - banh mi (Vietnamese sub, a tiny bit exotic but not weird) from Mei Sum Bakery in Chinatown. Cheap (three bucks) and delicious.
Early dinner on Newbury - La Voile. Authentic Provencal (as in the restaurant used to be located in Cannes) with a nice patio.