John 19:29 says (in the New International Version), "A jar of wine vinegar was there, so they soaked a sponge in it, put the sponge on a stalk of the hyssop plant, and lifted it to Jesus' lips."
Anyone familiar with Roman toilet habits would admit that this is reminiscent of how Roman's would wipe themselves after defecating (by wiping with a sponge on stick, cleaned off in water, and kept in a jar of vinegar as an antiseptic). Now obviously we (probably) can't be absolutely certain of it, but was this sponge on a stick supposed to be alluding to Roman toilet habits, by the writers of the New Testament, or was there actually some sort of tradition of giving individuals being crucified a drink?
In the ESV, Matthew 27:34 reads:
they offered him wine to drink, mixed with gall, but when he tasted it, he would not drink it. source
The "sour wine" referenced in John was most likely Posca, which was a sour wine beverage that was a common drink for the average Roman soldier, a mixture of sour wine or vinegar, water, and herbs. source
I'll quote a bit from here simply because it concisely lists some primary sources for further reading (and some recipes), whereas the Wiki link above gives the TL;DR:
Basically, we know that soldiers were given a vinegar ration (Vegetius, Concerning Military Matters, 3.3), and that this vinegar could be mixed with water and drunk. (Celsus, On Medicine, 2.27) Hadrian drank posca to 'be one of the soldiers' (Historia Augusta: Hadrian, 10.2), and from this we can infer that it wasn't a drink usually served to the rich. On the contrary, this was a drink sold on the streets! (Suetonius, Vitellius, 12.1)...
Clearly posca was good enough to keep a Roman army marching - in his soldiering days, Cato the Elder drank posca to fend off raging thirst. (Plutarch, Cato the Elder, 1.10)
Gall is believe by many historians to be referring to the poppy/opium.
Furthermore Miss Walker [138] states that the gall which was added to the vinegar was the juice of the hypnotic poppy, called rosch in Hebrew. source: Section The Poppy and the Hebrews
I know of no historian who suggests that the New Testament writers were making an allusion to Roman toilet practices. In fact, this sounds more like a literary device that we would put into a book today, rather than what someone living near the time of Christ would have invented in what purports to be a historical account. Leaving aside the historicity of the crucifixion narrative as irrelevant, I doubt the authors were trying to make a literary allusion, and the practices of the day point to more practical reasons.
As far as the sponge on the stick, the explanation I have heard is this was for practical reasons. If you have someone who is crucified, you can't just walk up to them with a bowl of wine with a bendy straw. The sponge would allow you to soak the liquid into it, and the stick would allow you to hoist the sponge up to the condemned who could suck on it. Simple as that. (I can look for a source on this if necessary.)
Here's where by necessity some exegesis comes in, I hope you indulge the source which is obviously not rigorous, but it speaks to how modern Christians interpret the meaning of the scene.
It was the custom of the Romans to offer a man being crucified drugged wine so that he might more easily endure his cross. Jesus refused the wine, however, apparently so that He could go through his suffering with a clear mind. source
Hope this helps and that I have followed all the rules (this is my first top level post here.) If I missed anything or made any errors, please let me know.
I wrote this in reply to a now deleted comment saying that the vinegar is "traditionally fulfillment of Psalms 69":
Saying "traditionally" is misleading. That implies that, say, the early church fathers gave us that explanation. Instead, John specifically says it is prophetic fulfillment (19:28-29), and while the historicity of the event is called into question, it's purpose for inclusion hasn't as the author of John tells us why he included it.
28 After this, when Jesus knew that everything was now accomplished that the Scripture might be fulfilled, He said, “I’m thirsty!” 29 A jar full of sour wine was sitting there; so they fixed a sponge full of sour wine on hyssop[h] and held it up to His mouth. (HCSB)
I couldn't find reference to this in the early church fathers (e.g. Justin Martyr, Irenaeus, Tertullian), but Cyril of Alexandria (c. 5th century) mentions it in his commentary (Book 12, p. 636):
of His own Will. Then He sought to drink; but so pitiless and far removed from the love of God were they, that, instead of liquid to quench His thirst, they gave Him something to aggravate it, and, in rendering the very service of love, committed a further act of impiety. For, in acceding at all to His request, were they not assuming the appearance of affection? But it was impossible that the inspired Scripture should ever lie, which put into the mouth of the Saviour these words concerning them: They gave Me gall to eat, and when I was athirst, they gave Me vinegar to drink.
That isn't interesting commentary, but worth mentioning, I suppose.