Two simple words that can mean so much. I have read how people want to spiritualize these words and what they mean. But, I think the simple answer is just as powerful.
The fact that Jesus was God in human flesh is fundamental to what Christians believe. This is yet another example of how Christ showed His humanity. He was hanging on a cross with real pain. As a man, Christ was thirsty.
These two words in John are preceded by the phrase, “After this, Jesus knowing that all things were now accomplished, that the scripture might be fulfilled, saith…” As the divine author of the Bible, Jesus knew the scriptures. He either said these words because He knew the scriptures. Or, as the inspiration behind the Bible, He had the Psalmist write his prophecy because He knew He would utter these words from the cross.
They gave me also gall for my meat; and in my thirst they gave me vinegar to drink.