I take Luigi with me all the time in his little purse. I've taken him to the mall, El Pollo Loco (haha), Whole Foods Market (they said no pets too..but he's so tiny and he stayed in the purse and I was there for 2 seconds, so what the heck), etc.
So yes, I do sneak him in. He's so tiny, I could even be blatantly holding him if I wanted to & it takes awhile for people to notice. Sometimes if you get a good carrier that looks like a purse, people will have no idea.
Only place I couldn't take him..Goldenspoon (frozen yogurt place that I love). Had a "no pets" sign on the window, and I wanted to be good, so I let my little sis wait outside with him