Are we sure we didn't just mishear and Sakura ins't sevenTEEN, but sevenTY? Because "A reusable bag!? They fold up that small now!?" is the most boomer-ass thing I've read in a long while.
It's really going to depend on where you shop and how long it's been since you've had to replace your bags. I've been using the same one for years, and it was secondhand when I got it, so I was pretty far behind the curve when I went reusable bag shopping a few months ago. At which point I had basically the same reaction as this girl half my age.
Tl;dr: Okay kiddo calm down
*calling it now: this is foreshadowing for her being some sort of designer baby bioengineered to become the ultimate assassin or something ridiculous along those lines.
She's definitely either a designer baby, kidnapped offspring of a super, product of a supernatural event, and/or put through esoteric training methods in an attempt to make something. Tiny chance maybe just held as ransom to keep someone else under control, but probably not since she ended up with Ruka and company rather than whoever they were ransoming her to. Though given the manga's unwillingness to give us the faintest detail thus far save for name-dropping The Facility (TM), I doubt it'll ever elaborate.