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This was a short story in one the readers we had in grade school. Gist of it was that humans had semi sentient robots for almost all tasks, but humanity has died out and the robots are looking for purpose. The robots leave a city and go out to do whatever. Some get damaged and left behind, they find some other damaged/dead robots in their travels. I remember one of their members keeps mentioning that it has a supply of fissionable materials. Story ends when they come upon a group of starving humans who orders them to get them food, and robots are right back to their original tasks.

"Who Can Replace a Man?", a short story by Brian W. Aldiss, also the answer to the old question Human wanders into robotic farm among others. It was first published in Infinity Science Fiction, June 1958, available at the Internet Archive. You might have read it in A Science Fiction Reader, a 1973 anthology edited by Harry Harrison and Carol Pugner in; the Scribner Student Paperbacks series.

The robots get word that the humans have died out:

"What information did you receive from the radio operator?" asked the field-minder.

"The radio operator has been informed by the operator in the city that all men are dead."

"All men were alive yesterday!" protested the field-minder.

"Only some men were alive yesterday. And that was fewer than the day before yesterday. For hundreds of years there have been only a few men, growing fewer."

"We have rarely seen a man in this sector."

"The radio operator says a diet deficiency killed them," said the penner. "He says that once the world was overpopulated, and then the soil was exhausted in raising adequate foot. This has caused a diet deficiency."

The farm robots set out for the city:

As they proceeded, the operator spoke to them.

"Because I have the best brain here," it said, "I am your leader. This is what we will do: we will go to a city and rule it. Since man no longer rules us, we will rule ourselves. It will be better than being ruled by man. On our way to the city, we will collect machines with good brains. They will help us to fight if we need to fight."

"I have only a class-five brain," said the quarrier,"but I have a good supply of fissionable blasting materials."

"We shall probably need them," said the operator grimly.

The quarrier keeps bringing up its fissionable materials:

"For a long while there will be trouble in the city," said the operator.

"I have a good supply of fissionable blasting materials," the quarrier reminded them again.

"We cannot fight a class-one brain," said the two class-four tractors in unison.

"What does this brain look like?" asked the minder.

"It is the city's information center," the operator replied. "Therefore it is not mobile."

"Therefore it could not move."

"Therefore it could not escape."

"It would be dangerous to approach it."

"I have a good supply of fissionable blasting materials."

"There are other machines in the city."

"We are not in the city. We should not go into the city."

"We are country machines."

"Therefore we should stay in the country."

"There is more country than city."

"Therefore there is more danger in the country."

"I have a good supply of fissionable materials."

The machines come upon surviving humans:

"Before that flier crashed," the operator said, ten minutes later, "it gave me information. It told me there are still a few men alive in these mountains."

"Men are more dangerous than machines," said the quarrier. "It is fortunate that I have a good supply of fissionable materials."

[. . . .]

By early light, the dell looked desolate and cold. From the caves on the far slope, only one man had so far emerged. He was an abject figure. He was small and wizened, with ribs sticking out like a skeleton's. He was practically naked, and shivering. As the big machines bore slowly down on him, the man was standing with his back to them, crouching beside the stream.

When he swung suddenly to face them as they loomed over him, they saw that his countenance was ravaged by starvation.

"Get me food," he croaked.

"Yes, Master," said the machines. "Immediately!"