I guess forests have seemed to be deep, dark, and dangerous for a long time. To say “We’re not out of the woods” is to say we remain in trouble, that we have not overcome “a dangerous, perplexing, or difficult situation.” dictionary.com

Abigail Adams used the expression in a November, 1800 letter found in Papers of Benjamin Franklin (ginger) but the phrase seems to be much older, though I didn’t find the specific citations:

This expression, alluding to having been lost in a forest, dates from Roman times; it was first recorded in English in 1792. dictionary.com

With the holidays upon us, suspicious gifts may arrive at your door. You might inspect a horse’s teeth to estimate its age and value. To do this to a horse that is a gift is ungrateful – although, I know something about what it costs to keep a horse, so a sad old plug is a gift you might refuse!

Knowyourphrase says:

John Heywood, who is thought to have lived from the years 1497-1580 C.E., is said to have wrote the saying in a book of his called A dialogue conteinyng the nomber in effect of all the prouerbes in the englishe tongue, 1546:
“Where gifts be given freely—east, west, north or south— No man ought to look a given horse in the mouth.“

Phrase Finder says “As with most proverbs the origin is ancient and unknown,” but also notes that Heywood collected exprssions in common use at the time, and didn’t claim to have coined them.

Heywood obtained the phrase from a Latin text of St. Jerome, The Letter to the Ephesians, circa AD 400, which contains the text ‘Noli equi dentes inspicere donati’ (Never inspect the teeth of a given horse). Where St Jerome got it from we aren’t ever likely to know.

To be over a barrel is to be helpless, at another’s mercy.

The Phrase Finder identifies this as an American expression from the mid-20th century, and refers to a cartoon from the Pennsylvania newspaper The Clearfield Progress in 1938.

Worldwidewords found an earlier citation: “Woodland Daily Democrat of California, dated January 1896: “To use a vulgar expression, a Republican congress gleefully assembled in Washington for the express purpose of getting President Cleveland ‘over a barrel.’ The humiliating predicament…” As often the case, it seems the writer expected his readers to recognise this easily.

The OED suggests that the allusion is to placing a person rescued from drowning over a barrel to clear their lungs of water. This might sound rather unlikely, but there are many references in the literature to show this was once a common practice…

 

There are instances recorded from this period and earlier of a person being placed on or rolled over a barrel as a humiliating punishment. One case was that of a student hazing at a college in Ohio, reported in the Frederick Daily News in Maryland in 1886: ‘Once inside he was at the mercy of his captors, and the treatment he received was cruel. Bound hand and foot, he was rolled over a barrel.’ This is by far the more likely origin, since a person held over a barrel is helpless, whether face down or face up. It fits the meaning of the phrase much better than the resuscitation one does.

To cross a bridge when you come to it means to deal with a problem when it is imminent. A related phrase advises, don’t cross the bridge till you come to it, changing the meaning to say don’t worry about a problem that may not arise, or don’t allow a future problem to divert your attention from current needs.

Theidioms puts the origin of the phrase in the 1800s, when there was often literal concern over the safety of bridges.

The reliable Phrase Finder had a post asking about the phrase, but no information on the origin.

Wikipedia lists it as an English proverb, so I suspect it is recorded in old books, but none is listed.

So I tried searching on “Guttenberg ‘cross the bridge till you come,'” and found The Golden Legend, a poem from 1851 by Henry Wadsworth Longfellow. Included in a conversation with Lucifer:

That, my good woman, I have not said. Don’t cross the bridge till you come to it. Is a proverb old, and of excellent wit.

So apparently the saying was well known by 1851.