While Maya Angelou did not call herself a Christian, believing that ‘calling yourself a Christian was referring to something that was complete, rather than a work in progress’ she certainly tried to become one, which may be relevant to the couplets about bread and water.
In an interview in the LA Times in 1992 she said:
I have always tried to find myself a church. I have studied everything. I spent some time with Zen Buddhism and Judaism and I spent some time with Islam. I am a religious person. It is my spirit, but I found that I really want to be a Christian. That is what my spirit seems to be built on.
On this basis there is a possible spiritual reading of the poem, it doesn’t say so much that we need human company, after all the millionaires have wailing wives and singing children, but that our souls need a home, and she has expressed that hers finds its home in Christianity, with the Christ.
The specific reference to bread may be to verse 4:3 in Matthew
Then the devil came to him and said, "If you are God's Son, tell these stones to turn into bread,”
The verse is part of the telling of the temptation of Christ during his 40 days in the desert. Jesus’ response in the story is to tell the devil that
"The scripture says, 'Human beings cannot live on bread alone, but need every word that God speaks.'"
So, when the poem says that her soul needs a home where bread is not stone, it may mean a world where the devil doesn’t win. In God’s house bread is bread (or even the body of christ) and nourishes us, in the devil’s abode the bread is stone and does not nourish.
In another poem, named - despite her claim elsewhere to not calling herself a Christian - ’I am a Christian’, Angelou writes:
When I say... ‘I am a Christian
I’m not bragging of success.
I’m admitting I have failed
And need God to clean my mess.
This reinforces the interpretation of Angelou as a spiritual person who sees the need for God’s infallibility in a world where humans mess up.
The water reference is possibly more clouded by poetic use of language, but it may be that in personifying water, by ascribing it the quality of understanding thirst, she is referring again to biblical verse. A strong candidate would be the reference to ‘living water’ at John 7:38
Whoever believes in me, as the Scripture has said, will have streams of living water flow from deep within him.
On this interpretation the overall theme of the poem would be that whatever strife is coming mankind’s way, faith will help us more than wealth.