I have read the debate in this thread and I have to agree with Tracy W. The reference to "stock" would of course normally refer to food and supplies, but you seem to be taking it out of context. One must read a whole paragraph, minimally an entire sentence before judging the meaning of a phrase. Let's reflect:

"They were just approaching the house where lived Mrs. and Miss Bates. She determined to call upon them and seek safety in numbers. There was always sufficient reason for such an attention; Mrs. and Miss Bates loved to be called on; and she knew she was considered by the very few who presumed ever to see imperfection in her as rather negligent in that respect, and as not contributing what she ought to the stock of their scanty comforts. "
The subject of the paragraph as a whole is clearly visiting. And if that is not enough to determine what JA is referring to, consider the sentence--(paraphrasing) You can always come up with a good reason to visit, the Bates like to have visitors, and Emma knows that people who can see her flaws consider her rather negligent in THAT RESPECT (i.e. VISITING), and not visiting them as much as she should, which is one of their few and pitiable comforts.
It seems pretty obvious to me that the subject is quite clear. If we held every author to literal interpretation, reading would be a bore.
Speaking of a bore, Miss Bates is beyond a bore--she's intensely annoying and rude in her own way; she never allows anyone get a word in edgewise. While I do in fact think Miss Bates is a sweet character and Emma should do her duty, give her a break! How many of you here actually spend much time with people you can't stand? Of course it is a nicety to do so, or SAY that we do, but let's be realistic. Most people do not put themselves in the way of those they do not enjoy being around unless they have no choice in the matter (i.e. they work or live together, they're relatives, or at mutual social functions).
I have to say it was a relief to me to read Tracy W's posting, because it was getting quite stuffy in here with the rather extreme expectations put on human feelings and behavior.