Moed Katan, Chapter One, Mishnah Ten
The final mishnah of this chapter introduces two more categories relevant to the laws of the festival. While some work may be done during the festival, one should not leave work for the festival that could have been done beforehand. Second, one should not use the festival as a time to prepare things for after the festival.
1) They may put up a railing around a roof or a gallery porch, in the style of an ordinary person but not in the style of a professional.
2) They may put plaster on crevices [on the roof] and flatten them down with a roller, by hand or foot, but not using professional tools.
3) A hinge, a socket, a beam, a lock, a key which brokethey may repair them during the festival, as long as he doesnt intend to do this work during the festival.
4) And all the pickled food that he may eat during the festival, he may pickle.
Section one: It is permitted to put up a railing on a roof or a second-floor porch, but only if it is done in a non-professional manner. For instance, putting up a rough stone fence would be permitted, but a nicely finished iron fence would not.
Section two: This refers to fixing a roof. It is permitted to fill in the crevices and to flatten the plaster, but not with professional tools. The central idea is that work that needs to be done should be done differently during the festival.
Section three: If a part of a door broke (these are all parts of a door), it may be fixed on the festival, and in the normal way. There doesnt seem to be any non-professional way of fixing the door and hence all ways of fixing the door are okay. The mishnah does, however, offer one reservation. He may not delay fixing the door until the festival, saving his work for when he has more time. The door should only be fixed if it actually broke on the festival, an unforeseen problem.
Section four: He can pickle food on the festival, but only if he is going to actually be able to eat the food during the festival. He may not use the festival as a time to prepare for the future. Note how this section is the mirror image of section three. There we learned that a person may not save for the festival work that should have been done before the festival. In this section we learn that a person may not do work on the festival for after the festival.