This is an interesting question. I’d wager that most readers initially make a contrast between the bread and coal in the angel’s hands as representing rewards for good and evil. We know about the bread of the Covenant at the Last Supper. And no doubt most of us have heard about getting a lump of coal or two in your stocking if you were a bad boy or girl. Alternatively, as the OP stated, the two items may also represent a tradition between the well-to-do (bread) and the poor (coal).
There is a another historic symbolism of the bread and coal that is somewhat different. The two items of bread and coal may essentially represent the same singular idea; that is, one of redemption.
The origins of Christmas trees are widely known and are not important to the question. As to an angel tree topper, its first use apparently sources to the United Kingdom’s Victorian Era from about 1837 to 1901.
The Illustrated London News published a picture of Queen Victoria, Prince Albert, and their family around a Christmas tree topped with an angel, and by its influence the Christmas angel became the most common tree-topper.
If you enlarge the picture of the angel on top, you find it dressed in red and white. It appears to hold somethings in its hand and one could easily hazard a guess that it is bread (right) and coal (left).
Why an angel in the first place? The idea is consistently one of a herald, a messenger. What is the message? The answer, the symbolism is in the bread and coal.
When did the angel first appear with two items in its hands? The answer is more of a mystery, but one that is inferred from when it first appeared.
HEAVEN or HELL
Before looking at the bread and coal as the same metaphor, there are traditions that the two are very different states of mankind or even of Christians! Keep in mind that apparently the angelic tree topper appeared about the same times as our sources.
Charles Spurgeon an English preacher (1834-1892) contrasts a type of bread and coal as in the same house, though different implications.
I believe that most of God's children sometimes get down in the dumps. There is a coal cellar to God's house as well as a banqueting hall and, although I should like to always live in the banqueting hall, I have many a time been down in the coal cel-lar—and I have learned more, there, than I have learned upstairs!
Spurgeon, Sermons 45
This idea of partaking of either bread (good) or coals (bad) may be traceable far back in time to Pseudo-Dionysius circa CE 600.
This sacrifice [of Christ’s death], here celebrated, we commemorate to Thee, O Lord, and the sufferings which Thou didst endure on the Cross for us. Be propitious, O Good, and Lover of men, in that hour full, of fear and trembling, to this congregation of those adoring Thee, and to all sons of the holy Church, bought by Thy precious blood. May coals of fire be kept from those who are tinged with Thy blood, and sealed by Thy sacraments in Thy holy Name, as formerly the Babylonian flame from the youths of the house of Hanania;
It is also interesting that Parliamentary Papers from that Victorian time period mentions tickets issued to the poor who could redeem them for both bread and coal. With this, we find that the two items are essential symbols of life. This too may have influenced our traditions. See page 850.
Lastly, in keeping with the idea that the two items represent symbols for good, we may cite from the bible where Elijah is running from Jezebel.
And as he lay and slept under a juniper tree, behold, then an angel touched him, and said unto him, Arise and eat. And he looked, and, behold, there was a cake baken on the coals, and a cruse of water at his head. And he did eat and drink, and laid him down again.
In this story we have the traditional evergreen, the angel, bread (cake) and coals.
In all of these traditions, the one constant is the angel heralding and holding or providing two items. Were the items it held a contrast of bread for good and coal for bad or were they symbols of the same reality; that is, bread and coal as necessities for life?
The angel of course represents the heralding angel. Hark, the herald angel sings, glory to the newborn king. The bread of heaven had come to earth.
And the angel said unto them, Fear not: for, behold, I bring you good tidings of great joy, which shall be to all people. For unto you is born this day in the city of David a Saviour, which is Christ the Lord. And this shall be a sign unto you; Ye shall find the babe wrapped in swaddling clothes, lying in a manger.
For the bread of God is he which cometh down from heaven, and giveth life unto the world.
Hark Emmanuel, God with us. But hark too our reaction. Mine lips are deceitful and evil, I am a sinner, how can I receive this gift of life? Religious traditions answer in different ways from universal salvation to working for salvation. Again, this is unimportant to the question. For this angel tradition though, there is only one answer. The angel offers bread and uses the coal to one who acknowledges his/her sins.
Then said I [the prophet Isaiah], Woe is me! for I am undone; because I am a man of unclean lips, and I dwell in the midst of a people of unclean lips: for mine eyes have seen the King, the LORD of hosts. Then flew one of the seraphims unto me, having a live coal in his hand, which he had taken with the tongs from off the altar: And he laid it upon my mouth, and said, Lo, this hath touched thy lips; and thine iniquity is taken away, and thy sin purged.
We have seen angel toppers clothed in either white or red to explain that symbolism. Keep in mind that these were Protestant preachers. So although he does not tie this with an angel topper necessarily, Scottish preacher George Adam Smith (1856-1942) will put it, bread represents redemption, but so too the coal as the means.
[Isaiah’s vision] for so simple a process of atonement leaves out the most characteristic details of the Jewish ritual of sacrifice, while it anticipates in an unmistakeable manner the essence of the Christian sacrament. In a scene of expiation laid under the old covenant, we are struck by the absence of oblation or sacrificial act on the part of the sinner himself. There is here no victim slain, no blood sprinkled; an altar is only parenthetically suggested, and even then in its simplest form, of a hearth on which the Divine fire is continually burning. The glowing stone, not live coal as in the English version, was no part of the temple furniture, but the ordinary means of conveying heat or applying fire in the various purposes of household life.
The stone/coal was applied, not something taken or achieved.
With these things in mind from the same period, we thus find traces of the different ongoing traditions of an angelic tree topper clothed in white or red or both who holds bread in one hand and coal in the other.
Those traditions offer different understandings that range from contrasting bread for good and coal for bad to finding both bread and coal as symbols of good or the necessity of life. Lastly, we find the heralding angel who announces Christ the bread of life and the coal of simple application. For this tradition, the angel with bread and coal is not a contrast of people or symbols, but a compliment of Christian reality foreshadowed and fulfilled.