Worked in Back Bay for almost 7 yrs, so I hear you. Not sure if you only mean take out places, or any general suggestions, but some places I'd eat at:
Laurel's - great value, can be busy at lunch
Shino Express - cheap, passable sushi
Douzo - more expensive, better sushi/japanese (but not outstanding imho)
Chili Duck on Boylston - good Thai
Thai Basil on Newbury - Chili Duck is better, but this is closer if you're near the Gardens
Kashmir lunch buffet - loved this when I want lots of food
Piattini - the one on Newbury; Italian - with nice selection of pastas, sandwiches and salads
Boloco (used to be The Wrap) on Newbury - for decent wraps (never had their burritos)
Shaw's Market for their salad bar - it's a pretty decent salad bar, and has a nice selection of sandwiches & cooked food too
Not claiming these are must try lunch spots, but they offer a nice variety.
Personally, I used to walk to Chinatown a lot for takeout (especially for bahn mi). It took about 20-30 mins top round trip.
If you're eating at Viga and Rebecca's it sounds like you're more towards the Arlington end of Back Bay.
I would second the recco for L'Aroma. Another one close by is the Berkeley Perk Cafe - on Berkeley Street, just over the bridge over the Pike, on the left. They have great sandwiches.
Take out from the Crossant de Jour place in the Park Square building is always decent, and they do a great BLT. I also like their Greek salads. And while the market is open, sandwiches from Iggy's food stand in Copley Square (Tuesday/Friday) are great and a real bargain at $5.
Kaya does a nice sushi lunch - miso, 6 nigiri and a tuna roll, or three different maki rolls, for $10, and they do takeout.
I've worked in Copley Square for 25 years and am VERY bored by the lunch options.
THE UPPER CRUST on Newbury (near Exeter) serves fantastic pizza, by the slice or by the pie. Plus their salad has nice, real cheese.
BRASSARIE JO has 5 or 6 excellent sandwich/salad/soup/frite specials. Sometimes service can be slow, though.
The buffet at the AU BON PAIN in Copley Place is sort of bizzare but good if you can't make up your mind about what you want.
DAVIO's take-out stall has good sandwiches and pizza and a daily pasta special. It's in the office building.
FLASH's on Stuart St. is still good, though I bet few people remember when it was a greasy spoon that served grilled cheese and burgers on plastic trays.
B. GOOD on Dartmouth by BB Station is a love-it-or-hate-it kind of thing. I'm in the latter camp, but others I know like it a lot.
If you have at least an hour, jump on the T and go to CHEF CHANGS in Brookline (C line, first above-ground stop). Their food is fantastic and their lunch specials are the best deal in town.
And, horror of horrors .... there is now an Applebee's in the Pru mall.