(Wow, if you look at the word contemporary for too long it starts to seem like gibberish, doesn't it?)
OK, first of all, I write either ancient world fantasy romance or science fiction romance. Therefore what's contemporary to my characters in 1550 BCE Egypt or the very farflung future probably won't take you out of the story. You won't get sidetracked remembering when you wore that to junior high school or snicker at my referencing something your Mom liked in the Dark Ages Before the Internet. Unless you're immortal or a time traveler from the future. In which case, I want to hear from you!
For example, in Magic of the Nile, this is about as risky-contemporary as I get:
After they’d finished eating, he escorted her to the square to watch a performance of the old scribes’ tale “The Shipwrecked Sailor”, put on by a traveling company. Tyema laughed and applauded along with everyone else. She couldn’t remember an evening where she’d just had fun, or felt so at ease.
“I’ve been shipwrecked and let me tell you, it isn’t nearly as entertaining as these players make it appear,” he said in her ear as they left the play. “Of course the island I washed up on had no fifty foot talking snakes, no enchanted dancing girls, nothing but scrub palms and sand.”
Seen "The Shipwrecked Sailor" by Anonymous recently? No, I didn't think so. And actually, I have no idea if the very famous story ever was enacted by anyone along the Nile, traveling or not, but it is a dramatic tale, often cited. I felt for the purposes of my novel, however, I could be a bit anachronistic and let my hero and heroine see a performance during the evening under discussion.
If I'm reading a classic romance novel - a vintage Mary Stewart, for example (my favorite is This Rough Magic, with Nine Coaches Waiting a close second) - it may be a bit jarring to me to have the characters smoking up a storm, and talking about things that are long passe now, but I know I've picked up a book of its time and I turn off my nitpicky brain. I go for the ride and the romance.
To be fair, if I wrote contemporary 2015 novels, it probably would be quite a challenge not to inadvertently fall into mentioning actual brands/bands/whatever, because they’d be part of the world the characters moved through. And I’d want the world to feel realistic to me and to the readers. But it does bring the risk of an author’s novel going flat the day after release if they happen to have sent their characters shopping at a store that just now declared bankruptcy and put a zillion people out of work with no notice, or talking about a favorite sports hero who just got arrested in our Real World for some highly incriminating viral video of Unspeakable Acts. I think I’d probably go for the same technique I use in my science fiction, which is to make up company names and celebrity names and brand names and quote no song lyrics, and remember that it’s all a work of fiction, right down to the allegedly gilt-edged names on my pages.