What I'm hearing is "teachable moments".
First, while it's tempting to shield your child from advertising, I think it's a mistake to do so completely. Instead, start looking at ads together and discuss with her what they're trying to make you believe. We're ALL influenced by ads, so it's right to help her, to "walk her through it" and help her see what they're promising vs. what the item can deliver. This is a skill that she needs to develop, and she probably needs your help to get started viewing ads with a critical eye.
She can probably "see" the truth in ads for products that don't appeal to her /aren't targeted at her. Cigarette ads would be a good starting place. Show her a picture of the Marlboro man in his cowboy duds. Ask her what the ad is promising: If you use this product, you'll be good looking, tough, independent, strong, sexy. She's old enough to see that this picture appeals to men -- even if they don't want to be cowboys personally. Then ask her what the product actually delivers. She should see a big difference. Then show her a product for some sort of convenience food: It'll probably show a woman surrounded by a family sitting down at the table with appreciative looks on their faces. Ask her what they're selling: Buy our chicken nuggets, and your clean, well-mannered children (and their father) will rush to the table and look at you as if you're a goddess for popping some chicken nuggets in the oven. They're selling the promise of a happy family. Again, she should see that the reality doesn't really match the promise. Once she can see those differences ... then it's time for her to look at ads directed at her. Once she's started to see the truth, she'll approach ads with a more critical eye.
Don't think that she won't continue to be tempted: We all are. You'll have to continue to repeat this lesson over and over; after all, the advertisers are providing plenty of follow-up with their lessons!
Second, she's at a normal age to start comparing herself with other kids. You have to walk a fine line here. You don't want to dismiss her comments with a quick, "Oh, we can't afford that." For one thing, it's probably not true. For another, it can make her worry that you may not have enough money to survive. Yet you also don't want to squash her dreams and make her feel that she can't express her thoughts and desires to you.
When my kids were going through this stage (and it is a stage), I often looked at the item they said they wanted and agreed with them, "Yeah, it would be nice to have _____, wouldn't it? I bet it'd be fun. But that's not how Daddy and I choose to spend our money." This acknowledges that, yes, nice things are -- well, nice. You're not wrong or bad to want things (that's what I was told growing up, and it's not a good thing to tell a kid). But we have limited resources, and Daddy and I have made choices. OFTEN that launched into good discussions about quality vs. quantity, saving vs. spending, and having enough. Teachable moments.
Your daughter isn't "there yet", but I see kids at school and through the youth groups with which I work who -- maybe in late middle school through early high school -- pick up the idea that WOW, there's GOOD STUFF OUT THERE! And if my parents don't have it, they made sucky choices. Often they start to get the idea that their parents are idiots for not grasping that they could've CHOSEN BETTER! This is kind of the start of the parents-are-stupid-because-I'm-a-teen-thing. They start in on the big-unattainable-dreams-unconnected-to-reality: They're going to become rock stars, models, NFL players, and then they'll have several mansions across the globe as well as a fleet of sports cars, etc., etc., etc. Basically, they start to imagine themselves as Kardashians. Did I spell that right? They get this idea that ANYONE can do these things -- you just have to be smart enough to choose right! And the kids who get big-time into these ideas tend NOT to see their own efforts and abilities as being tied into those choices. A kid who's more grounded in reality may flirt with these ideas, but it'll be fleeting moments rather than a genuine belief.