I heard that there is a custom to buy a new kitchen knife every year for use on Rosh Hashanah. Did you ever hear of this, and, if so, what is the reason for this tradition?
Though this is not a common custom, a little research confirmed the existence of such a tradition, and also provided its reasoning.
G‑d is the One in charge of everything, yet He does have a whole slew of ministering angels who carry out His orders.
"Chatach," (חתך), which means "cut," is the name of the angel in charge of livelihood.
Consider that the final letters of the Hebrew words, פותח את ידך, "You open up Your hand" (Psalms 145:16), spell "chatach." Additionally, the word that follows in the verse, "u'masbe'a" – "and satisfy [the desire of every living being]" has the numerical value of 428 – the same value as the word "chatach."
For this reason, purchasing a new, sharp knife is a segulah (spiritually propitious), for livelihood, which we petition from G‑d for the upcoming year.
May G‑d inscribe you and your family, and all the Jewish people, for a year abundant in livelihood—and everything good!
Best wishes for a good and sweet year!
Rabbi Eliezer Danzinger for Chabad.org