Irons in the fire. Branding irons? Going to iron clothing to remove wrinkles? Or for just plain irony.
That's the original expression, created way back when women heated clothes irons by the fire in order to press shirts. The iron would sit on a metal stand in the fire, so it would get warm without collecting soot or getting too hot. Our family always had plenty of antiques around the house, so I encountered several of them and am familiar with the practices. We also had butter churns and hand-cranked coffee grinders made into tables.
While not exactly a crossover, I have something that happened in my first story effecting a character in a story I am currently working on.
Technically, I'm not sure that's a cross-over, instead it's a 'common event' between the two stories. A cross-over (I believe) is when characters from one story cross-over to another (as if they physically walk between the two books). If you have multiple stories that revolve around the same event, using different characters, then you've got a universe (even if it's not open to other authors).
Every place I have ever been has its own local businesses which are similar to both types of business. If unsure what is popular in a specific region, just ask maybe someone here will know enough to help out. Or look at businesses in the region listed in the Yellow Pages on the internet. Use them if needed to substitute. In some ways it will be just free advertising for their business.
I was asking whether any other authors had a nationwide chain I could include in my stories, rather than continually hawking the same commercial chains over and over. Though if I did that, I'd have to explain in the context of the story how the chain got started for any non-SOL readers who discover my books (I've got several readers who've discovered my works from Amazon sales).