I wouldn't take them to any pet store that sells rats as the risk of exposure to viruses is very high.
I would not take my pets to any store where pets are not allowed.
I would worry way too much about taking them in public places like parks or such. I worry sometimes when I take my 10lb dog out because people are morons and loose dogs are super scary. My small rat could get loose or injured so easily. It just is not worth the risk to me.
I like bringing my rat over to my mom's house for brunch. Mom lets me put her carrier on the table and Nanook comes out and samples the pancakes and fruit. It's pretty fun.
I've also taken her to an open air market where everyone fussed over how pretty she is.
Most frequently we go for evening walks around the neighborhood. I'm always slightly concerned that a hawk might grab her off my shoulder, so she hides under my hair or else I end up holding her in my arms (which she loves!).