Sifrei Mitzvot untuk Imamat 23:27

There is a positive commandment to rest from labor on the tenth of the seventh month [Tishrei], as it is stated (Leviticus 23:32), "It shall be a Shabbat of rest for you." And anyone who does labor on it has negated a positive commandment and violated a negative commandment, as it is stated (Numbers 29:7), "And on the tenth. etc. you shall not do any labor." And what is he liable for doing labor on this day? If he did it willingly and volitionally, he is liable for excision. But if he did it inadvertently, he is liable a fixed sin-offering .

Whenever the penalty for work done willfully on the Sabbath is stoning, the penalty for doing it willfully on Yom Kippur is kareth; whenever the penalty on the Sabbath is a sin-offering, the penalty on Yom Kippur is equally a sin-offering. Anything that must not be done on the Sabbath, though it is not actual work, must not be done on Yom Kippur; if one nevertheless performs it, he receives punishment for disobedience, the same as he would for a similar act on the Sabbath. And whatever is forbidden to move on Shabbat is forbidden to move on Shabbat. And whatever is forbidden to say or do at the outset on Shabbat, so is [it] forbidden on Yom Kippur. In brief: The only difference between the Sabbath and Yom Kippur in this respect is that the punishment for deliberate work on the Sabbath is stoning, while on Yom Kippur it is kareth.

It is permitted to trim a vegetable on Yom Kippur from the afternoon prayer and on. And what is trimming? That he removes the rotten leaves, chops the rest and prepares it for eating. And likewise is it permitted to crack open nuts and break open pomegranates from the afternoon prayer and on because of the anguish of the soul (i.e. so one won't have to do it after the fast when he is very hungry). And Yom Kippur that come out to be on Shabbat is forbidden for trimming a vegetable, cracking nuts and opening pomegranates the whole day. But the people of Shin'ar (Babylonia) and the West (the Maghreb) have already accepted not to do any of these [activities] on the day of the fast; but rather it is surely like the Sabbath in all of its matters.