There’s also a Venus Café at Black Pool Sands on the coast road between Torcross and Dartmouth. (as posted above by OCB whilst I was typing this!)
As mentioned above, The Curator in Totnes does the best coffee in town and has outside seating where you can keep an eye on your bike, and their outlet in Dartmouth, Woodroast does the best coffee at that end of the river, but is less bike parking friendly, being on a narrow street.
The Castle Tea Rooms in Dartmouth, over looks the river mouth, does excellent tea & food, and has outside seating and great views.
The Anchorstone Café in Dittisham, has excellent riverviews and lovely food, but slightly more expensive drinks. You also have to cycle back up the hill out of the village, or get the ferry over to Greenway and carry on your ride from there.
There’s also a Venus Café at East Portlemouth, opposite Salcombe. Nice views over the estuary, good coffee and snacks, and you can hop over the estuary on the ferry to get back to continue your ride back towards Plymouth.
The Staverton Nursery café on the river near Totnes is basic but nice.
Other good cafes are available in the area but I’ve got to stop typing and get on with some work!