The Barthes essay is quite abstract, definitely harder to follow than the Watt, but hard too in the sense that it is virtually impossible to find genuinely "insignificant" details of the sort he designates!
I put together these three passages on a handout so that we'd have something to look at; to state the obvious, "the reality effect" is never relevant for first-person narration, so that the Defoe passage is already out of the question; in the second passage, we briefly think the shoes might be a "look at me, I'm real" detail, but the narrator immediately moralizes and "meaningizes" them for the reader; the third passage is closest to what Barthes is talking about, but shows with exceptional clarity how hard it is for novelists and novel-readers not to fold insignificant details back into the world of meaning (the notation of the cost of the postage tells us something about the family's precarious finances; Mr. Garth's saving the red seal for his daughter speaks to his warmth as a family man).
I walk’d about on the Shore, lifting up my Hands, and my whole Being, as I may say, wrapt up in the Contemplation of my Deliverance, making a Thousand Gestures and Motions which I cannot describe, reflecting upon all my Comrades that were drown’d, and that there should not be one Soul sav’d but my self; for, as for them, I never saw them afterwards, or any Sign of them, except three of their Hats, one Cap, and two Shoes that were not Fellows.
- Defoe, The Life and Strange Surprizing Adventures of Robinson Crusoe, of York, Mariner (1719)
Her trip to La Vaubyessard had made a hole in her life, like those great chasms that a storm, in a single night, will sometimes open in the mountains. Yet she resigned herself: reverently she put away in the chest of drawers her beautiful dress and even her satin shoes, whose soles had been yellowed by the slippery wax of the dance floor. Her heart was like them: contact with wealth had laid something over it that would not be wiped away.
- Flaubert, Madame Bovary: Provincial Ways, trans. Lydia Davis (1859)
In watching effects, if only of an electric battery, it is often necessary to change our place and examine a particular mixture or group at some distance from the point where the movement we are interested in was set up. The group I am moving towards is at Caleb Garth’s breakfast-table in the large parlour where the maps and desk were: father, mother, and five of the children. Mary was just now at home waiting for a situation, while Christy, the boy next to her, was getting cheap learning and cheap fare in Scotland, having to his father’s disappointment taken to books instead of that sacred calling ‘business’.
The letters had come – nine costly letters, for which the postman had been paid three and twopence, and Mr Garth was forgetting his tea and toast while he read his letters and laid them open one above the other, sometimes swaying his head slowly, sometimes screwing up his mouth in inward debate, but not forgetting to cut off a large red seal unbroken, which Letty snatched up like an eager terrier.
-- Eliot, Middlemarch (1871-72)