If it's just me and I don't need to use the rack, I don't. It goes in the car. I left it unattended during lunch ONCE. Dh said it would be fine, but I went out way too much to make sure everything was still okay.

Won't do that again, even though everything was okay.

We were on a trip this past weekend, and I brought the bike (and I didn't have room to put it in the car with 4 people and baggage). When we stopped for lunch, we sat by a window so I could keep an eye on it.

You're not paranoid at all.