Unless you live under a (very litvish) rock you know that this week is Shlissel Challah Week. This is the segula that "everyone" does the week after Pesach, or more specifically, the week of Shabbos Mevarchim Iyar, for good parnassa.
Most people I know participate in this segula by baking challah for Shabbos with their home-key baked into the bread. I think this is the prevailing way of doing it, but I could be wrong.
A lot of people think there is no source for this custom. While early sources are scant, the Sefer Todaah, by Eliyahu Ki-Tov writes (and I paraphrase) that there is a custom to bake Challah in the shape of a key sprinkled with sesame seeds. The seeds remind us of the mon which began in Iyar and that is why we do it this week.
In general I shy away from placing too much weight in pure segulos. I call them "shortcuts". People want the "merchandise" without paying the "price". They think that God will grant them what they want if they perform some ritual. I say, let's get the basics right first.
This segula is even funnier. The only source I know for the segula (Sefer Todaah) says to bake the challah in the shape of a key. Yet, it seems that is just too hard for people. It's too much effort to fashion a challah in the shape of a key. So instead people take another shortcut and make the challah in the standard fashion and just bake the key into the challah.
The shortcut that the Sefer Todaah mentions is further shortcut by the recent innovations... I find that amusing. Maybe I just have a weird sense of humor...
Search for more information about super-duper shortcuts at 4torah.com.