I didn t pick upon some bough. We have established that the apple represents both life and death, and in this instance may we go even further and say that these particular apples represent life experiences, these experiences were missed. Or perhaps knowledge that was not gained, but was desired. Thus the barrels are empty, thus regret. Through this passage we see that he is reflecting back on his life.
Some experiences are clearer than others.
Perhaps some are more significant now than they were at the time. This reflection seems to not only depict his age, but also his regret. It is as if the speaker sees more than just himself in the reflection in the drinking through. He seems to be seeing visions of his life. Our speaker seems to be seeing all of his chances, or opportunities.