Coincidence as a plot element. True, chance encounters sometimes advance the action, but, as in Anne Elliot running into Wentworth at a pastry shop in Bath, they are never incidents that seem particularly unlikely.
Orphans of unknown parentage who turn out to be the children of someone significant to the plot. There is Harriet Smith, but wonderfully, we never learn whose child she is.
Garrulous, comic servants who slow the action down by telling long tales. Though I associate this with Cervantes, you will also find them in Fielding, Radcliffe and Edgeworth. Not to mention Dickens. The closest we get to a garrulous servant in Austen is the manservant of the Dashwoods, who shares with his employers his news of encountering Mr. Ferrars and his new wife, Lucy. It's worth reviewing what a masterpiece of economy that scene is, and admiring how effectively it keeps the suspense alive in a way that is tricky without actually being deceptive.
Fainting. "Run mad, if you chuse, but do not faint!" is the advice one heroine of the Juvenilia gives to another, and it is advice the authoress seems to have followed. Marianne Dashwood comes close to swooning, in her dreadful encounter with Willoughby in London. But doesn't. No one else I can think of ever faints, despite much provocation.
Bondage. Not a single character, with the exception of the unfortunate Eliza, lost love of Colonel Brandon's youth, is ever forced into an unwanted marriage, or forced into a carriage and carried off to a convent or a brothel. No one is ever even urged into an unwanted marriage, except perhaps Elizabeth Bennet, to Mr. Collins, by her mother, and that is played for laughs.
Supernatural elements. There really aren't any, except in Catharine Morland's imagination. No ghosts. No ominous portents, no shadows, no sinister monks, haunted houses or groans in the night.
Lost and found. No one loses a fortune and regains it, unless we count the widowed Mrs. Smith, who with Wentworth's help manages to regain control of her previously encumbered West Indian properties and thus raise herself from penury to a modest condition of self-sufficiency. No one's child or parent, thought to be dead, re-emerges at the end of the book, to great dramatic effect.
Her readers in 1813 might be just as baffled by Jane Austen as her readers in 2009, but in a different way. To them, perhaps, all these missing elements might make the novels seem strangely stark, passionless and dry. Certainly their lack annoyed the heck out of Charlotte Bronte.
Thus, although Jane Austen was in her personal conduct, and apparently in her political views, to the extent that we know them, conservative with a small c, it is fair to say she was wild at heart where literary conventions were concerned. I cannot help wondering how she would have turned out if she had been born into Fanny Burney's family. Or Mary Wollestonecraft's.