Pip brings the convict an unusually large amount of "vittles," including half a jar of mincemeat, a quantity of brandy, and a whole pork pie. The boy is taking a big risk by stealing so much from his sister, but his present concern is seeing that the convict is satisfied.
In Chapter 8 Pip writes:
My sister's bringing up had made me sensitive.
And he repeats this at the end of the same paragraph:
I was morally timid and very sensitive.
The convict does not realize what an impression he is making on Pip in Chapter 1 with all his terrible threats.
“You bring me, to-morrow morning early, that file and them wittles. You bring the lot to me, at that old Battery over yonder. You do it, and you never dare to say a word or dare to make a sign concerning your having seen such a person as me, or any person sumever, and you shall be let to live. You fail, or you go from my words in any partickler, no matter how small it is, and your heart and your liver shall be tore out, roasted, and ate."
The fugitive must be impressed with the feast Pip has brought him, which seems like more than even a man as hungry as himself could consume. It is because of Pip's bounty that Abel Magwitch will remember him for so many years. When he encounters Pip again in Chapter 39:
“You acted nobly, my boy,” said he. “Noble Pip! And I have never forgot it!”
Pip knows full well he wasn't acting nobly but acting out of terror enhanced by his timidity and sensitivity. So his sister's mistreatment ended up inspiring Magwitch to devote his life to making Pip a gentleman. His sister made Pip timid and hypersensitive. Thus he was especially susceptible to the convict's threats. This induced Pip to bring an exceptionally large assortment of vittles to the hunted man, to whom it seemed even more magnanimous because of his terrible hunger. And he remembered it as a noble deed which he sought to repay commensurately.