Ivan Denisovich and Fetiukov in the novel are opposite characters. Yet they share some similarities between these characters. There standards and morals are completely different however. Ivan is proud and honorable. Fetiukov is a weasel and a scoundrel. They are different when Caesar is smoking a cigarette and Fetiukov wants the last puff so he begs Caesar and stares at his mouth. However Denisovich is proud and will not look at his mouth and does not beg. Caesar then offers up the last of the cigarette to Denisovich. That is where there is also a similarity; both characters will get what they can when they can. But in this they also share a common bond of smoking. Something the prisoners can do that they could also do while not in prison, it is a kind of release.
Similarly you could say both Denisovich and Fetiukov are scavengers. Both characters doing whatever they can to improve their conditions; but each in their respective way.
While Fetiukov is busy preying on people's pity for extra bread. Ivan Denisovich is being proud and working for the things he wants. He puts all the extra time he can muster up into doing favors and making things for other people. He takes any odd job he can find to make some extra money which he in turns can use to buy his own tobacco. Fetiukov would ask other people for a bit of theirs.
Solzhenitsyn is making a point in this, that there is a wrong and right way to survive. The wrong way is Fetiukov's way and the right would be Ivan's proud way.