Heh, I've seen kids who don't look more than 14 (so, still some growing to do) on bikes more expensive than mine.
DBF was a Boy Scout, and did the cycling merit badge--except that one of his troop leaders was one of our sort, so they got really into it, and many of them ended up with expensive stuff. Not super-high-end or anything, but enough. DBF's wheels cost more than my laptop! They often stopped at fast-food restaurants, convenience stores, or fancier places to top up water bottles (being in AZ). They at least had the sense to leave a couple people outside watching the bikes while everyone else topped up all of the bottles/Camelbaks.
I'll admit that I don't own a lock (I need to change that!), and have often stepped into McDonald's or another place to grab water or food. But--I always leave the bike in sight of the windows, and I keep glancing at it. Or I ask someone if they wouldn't mind keeping an eye on it. (And one place I've stopped at is pretty much a hive of cyclist activity, so few people lock their bikes--there's always someone watching!)