There are several places in the valley where you can stop off for a snack, bar meal, formal dinner or afternoon tea. Check opening hours and seasonal openings.
From the top:
Honister 
Honister Slate Mine : Cafe, gift shop and activities
Seatoller
Glaramara house : Light lunches and scones
Stonethwaite 
The Langstrath Hotel : Bar meals, lunch and dinner
Longthwaite
Borrowdale Youth Hostel : YHA’s standard menu (Tex-Mex and Mediterranean) : Restaurant open to the public
Rosthwaite
Scafell Hotel : Formal restaurant for lunch or dinner, or the “back bar” for hearty pub grub
Royal Oak Hotel : Afternoon tea and scones
The Flock Inn : Open from February to November. Specialists in Herdwick products
Hazel Bank Hotel : Dinner; advance booking required
Grange-in-Borrowdale
Grange Bridge Cottage Tea Rooms: Traditional cafe and tea shop on the site of the previous village shop and post office.
Grange Café : Traditional tea room with home made cakes. Teas, coffees, snacks and ice cream
Borrowdale Gates Hotel : Fine dining in a village setting
Watendlath
Caffle House Tea Rooms: Traditional farm tea room near Ashness Bridge.
Between Grange and Keswick
Leathes Head Hotel : Dinner, advance booking necessary. 2 AA stars.
The Borrowdale Hotel : Famous for its Sunday Lunch carvery; also dinners, bar meals and afternoon teas. Dress code
Shepherd’s Cafe: Farm tea shop and B&B at High Lodore Farm; its cakes are highly praised
Lodore Hotel : still open despite ongoing renovations : dinners, lunch, afternoon tea, weddings and functions. Dress code
Mary Mount : Restaurant and bar meals. Conservatory windows look over bird feeders and Derwentwater.