Well, my mom does not put her purse on the floor because it is a commonly believed Brazilian tradition that if you put your purse on the floor, your money will disappear. And trust me she really believes and follows this. She says my grandma believes the same.
I encountered this superstition twice in my collection. First this subject said it was a Brazilian superstition and the subject told me that his mom and grandmother followed it, and that they believed that if you set your purse on the ground than your money would disappear. He said that his mother never sets her purse on the floor for fear of this.
I think that this superstition could possibly stem from an idea that the ground is the lowest point, and setting something as important as money down on the ground is sort of careless and disrespectful. I also think that his version could have something to do with lower mythology, and perhaps setting the purse on the floor makes it easier for trolls to come and steal the money and thus it would disappear.
The second time I encountered the subject said that it is a popular belief in Mexican culture not to set your purse on the ground, saying that it is considered bad luck because you will not receive any money. She was not sure of the exact reason why it had to do with the ground or anything, but that all of the women in her family followed it.
I think that his version is much like the first in regard to the disrespect and carelessness by setting your purse on the floor. For this I think that the ground being low has more to do with the bad luck aspect, as the setting the purse on the floor makes it seem as though you dont care about the money. Maybe the idea is that the fact that you are so careless and therefore you will not receive any money.
I think its interesting to see the difference between the two variants, one has the idea that you will not receive any money and the other is that the money you have will disappear. I looked up the superstition on the internet but could not find anything that stated why or the origin of it.