Having grown up poor myself and now moving in more affluent circles, I see these differences almost every day. Food is a big one. Most people remain forever attached to the kinds of foods they grew up with. A once-poor person might no longer like boxed macaroni and cheese or Taco Bell burritos, preferring more upscale versions of both, but a never-poor person will curl their lip in disgust at the very idea. How do you decorate (or not)? What kinds of vacations do you take (or not)? Are there any things that you hoard, even though there's no longer a point? How are your teeth? These little markers are everywhere, if you know what to look at. Even the fact that people don't talk about their childhood, especially what kind of schools they went to or what sports/activities (if any) they were involved in, can be a big tip-off. I can usually tell within ten minutes or so whether someone I'm talking to is once-poor or never-poor, even if they're both in the same economic stratum now. And I definitely feel more affinity for the first group.

BTW, a lot of these markers - especially food and hoarding - are pretty well known for people who survived the Great Depression, too. Those habits die hard.