The shabbos after Pesach is known as the "Shlissel Challah"
segula (omen). This erev shabbos many people have a minhag to
bake a challah with a key in it -- with the key wrapped in foil,
or shape the challah as a key etc. This is a segula for a good
parnassa.
It is a reminder that the key to our sustenance, our parnassa, is in
Hashems hands. Here is a link to an article on shlissel challah
written by Rabbi Yehuda Prero: www.torah.org/learning/yomtov/pesach/5761/vol7no04.html
Below, is information from the web pertaining to the shlissel challah.
For those who are fortunate enough to be around for this special
segula, please remember to add names of any cholim (sick) and/ or those
who would like to get married, have babies, etc.
Shlissel Challah (Shliss=key)
The minhag of women (or men) baking the house key into the challah on
the Shabbat following Pesach (also known as a shliss [=key] challah) is
explained with the following reasons:
1. Based on "e-chudo shel machat...," ("Open up, my darling..."--
Shir HaShirim 5:2), on which the Medrash states "Pitchu li petach
ke-chudo shel machat...," (cf. Shi HaShirim Rabbah 5, s.v. "Kol Dodi
Dofek") = something like "Open your hearts (in teshuvah) like the eye
of the needle, and I (God) will open the rest like [a very large
opening].
2. According to Kabbalah on Pesach the gates to heaven were open, and
following Pesach the lower gates are shut, and its up to us to open
them again, therefor on the 1st Shabbat we put the key on the challah
to show that through the mitzvah of Shabbat we are opening the locks.
3. In the desert the Jewish people ate from the manna until after
Pesach upon entering the land at which point they ate from the produce
of the land, and became dependant on their livelihood for the first
time (now they had no manna). The key in the challah after Pesach is a
request the God should open the Shaarei Parnasah (gates of
livelihood). Alternatively, the manna began to fall in the month of
Iyyar, and this Shabbat is always Shabbat Mevarchim Iyyar.