There are plenty of options:

• You can carry around a spare burner phone that is powered off. These are relatively cheap ($30 + the cost of your cell plan), and has the benefit of working even when your main phone dies. You can leave it charging in your car.
• You can carry around a cellular hotspot, such as one from the Calyx Institute. This also helps fund a pro-privacy organization, and this hotspot can be used to provide internet for multiple devices. See this video for more information.
• You can still call emergency services even without a SIM card.
• If there are public Wi-Fi networks nearby, you can connect to those in order to get in touch with people you need.
• You can ask anyone nearby for help. Whether it be borrowing their phone to make a phone call, using their phone as a hotspot, or having them help you directly.
• Hike to the nearest civilization for help.
• Wait for a bus to pass by, if they are in your area.
• Some smart cars have the option to call for help built-in.
• Use GrapheneOS with a carrier. It will still be much more private than using iOS, and you can disable the cellular radios when they are not in use by enabling Airplane Mode.

Even without any of those, the chances that you will be completely stranded with no one to help and no way to call emergency services are very, very slim. Privacy protects you from more likely scenarios, such as data breaches or identity theft.