Have a Backup Plan
You should also have a backup plan.
The iPhone 8 and iPhone 8 Plus haven't sold out but some retailers might not have a ton of stock on hand on release day.
The cheapest iPhone 8 models, the 64GB iPhone 8 and iPhone 8 Plus, could be in short supply at some retailers.
You might not get your first choice, especially if you show up late on release day, so you'll want to have a backup color or storage option, just in case.