What is the etiquette when staying at Walmart pkg lots

Thanks everybody!! We are mostly looking to stop and sleep. No cooking and camping or patio set up. I pretty much knew to ask if we can park there but wanted to see if I needed to know anything else. And we'd most likely buy food at the store while there.

Any other quick, free stopovers to sleep that are safe. We'll have the kids with us so don't want to be anywhere iffy. I'll look at Flying J and Cracker Barrel if there are any near where we think we might need to stop for the day to sleep.