Yes it is The Beggar's Opera.  Polly and Lucy are both rivals for Macheath's affection and one of them (I think Lucy) tries to poison the other with rats' bane in the gin.  Her drinking song is Come sweet lass, let's banish sorrow till tomorrow and the melody was used in one of the first batch of modern hymn books c 1965.

The other drinking song, for the men (Fill ev'ry glass for wine inspires us) was set by John Gay to melody which I have come across as a French Noel Quelle est cette ordeur agreable? now in Andrew Parrot's revised Oxford Book of Carols.

Very odd ecclesiastical associations.

But there are plenty of other driinking songs in proper operas, as well as your number 3.

And before any other G&S buffs mention it, there is a Teacup Brindisi in the Act 1 of The Sorceror, sung by the Rector at the parish bunfeast, laced with the fatal love potion.   Come pass the cup round, I'll go bail for the liquor.  It's stong, I'll be bound, for it was brewed by the vicar.

I don't know Tristan that well.  Do he and Isolde toast each other in style before knocking back the stuff?

Yes, they toast each other before drinking the love potion, but it's hardly a drinking song. I can think of one Wagner example though, where Daland's crew starts up a merry drinking song to try and counter the eerie one coming from the Flying Dutchman's ship.

There are a couple more Verdian ones, including possibly the most obvious in the genre.

Nobody has had a stab at No.3 yet.

Would that be the one in Otello, IGI?

Lady Macbeth sings a brindisi to distract her guests from paranormal phenomenon at the dinner table.

But IGI is angling for one SO obvious cough, cough...

(Just seen harpy say just that.  I will look up Grove on the name.)

Thank you very much for putting me out of my misery, Don B. And "bring dir’s" would mean something like the barperson's "here you go" as they hand you your half of mild'n'bitter?

brindisi (n) - reputedly the text of a two-word telegram ("Bryn dizzy") sent to the Royal Opera House by a famous baritone (although misspelt by an Italian telegraph operator),  explaining that his head was spinning and he'd be unable to appear in the forthcoming RING cycle (Groan's Dictionary Of Opera)

Piet the Pot, Prince Go-Go and Astradamors get Nekrotzar blind drunk before setting Mescalina on him in order to attempt to prevent the end of the world in Ligeti's Le Grand Macabre (at least I think that's the order in which it all happens). Whether or not their plan succeeds or not is another matter.