We spent about GBP 60 for two, with each having
1 main course, 1 soft drink, 1 cocktail
Cocktails were GBP 13 IIRC.
We ate in the restaurant opposite the bar, and the food and service was great (they have improved beyond all recognition from the first time we stayed there one month after opening). For breakfast, we used the Flounge, so can't comment on Sofitel!
There's not much in the way of "light snacks", so for sure, if I wanted something light I'd wander into M&S.
Also the room minibars are not stocked unless you pre-request it. But you're welcome to put your own things in the fridge, so picking up things at M&S / Smiths is a no-brainer for drinks.