If you say all 613 mitzvos before you eat your food its a segulah for cold food.
There’s a story behind that but I don’t remember it.
Also there’s a sefer called Minhag Yisroel Torah that brings tons of minhagim (its a set of four as opposed Ta’amei HaMinhagim which is only one) and discusses their sources. An interesting one that I rememebr for it is that he writes that the mekor for the ‘seichel’ part of seichel and gelt (by havdallah) is the SA (washing eyes for chavivus hamitzvah) but he couldn’t find any moekor anywhere for the gelt part and even gedolim who he saw doing it and asked said that they only did it because its a minhag even though they didn’t know the reason for it.
My grandmas favorite:
If you sit at the corner of the table u’ll be in shidduchim a long time.
Also, dont pass the baby over the table. (that one probably originated because there was hot soup on the table)
A cell phone can cause the Machla, because a certain gut once spoke on his cell phone and actually the Machla.
I know there are studies this way and that, but I actually saw a circulation with the above message.
A barking dog doesn’t bite.
I never tried it (from either angle).