Pirkei Avot chapter 5, mishnah 6 says:
Ten things were created at twilight of Shabbat eve. These are: the mouth of the earth [that swallowed Korach]; the mouth of [Miriam's] well; the mouth of [Balaam's] ass; the rainbow; the manna; [Moses'] staff; the shamir; the writing, the inscription and the tablets [of the Ten Commandments]. Some say also the burial place of Moses and the ram of our father Abraham. And some say also the spirits of destruction as well as the original tongs, for tongs are made with tongs.
Three related questions:
Why were these specific items chosen to be created just before Shabbat? Why were these items created specifically before Shabbat as opposed to some other time? Could the reason these items were chosen be that all of them (except the tongs) were "one time" use?