But - it's not easy! Here is a strategy that I think would work, but I'm struggling to find an appropriate device.
- Mobile phone WITHOUT a sim card (wifi only)
- VPN router, using coreboot, Intel Management Engine disabled
- Dongle with 3g using an unregistered sim card
- Power Supply / Battery
Yes it would be a pain to carry round, but as this becomes the standard, devices that combine a PSU, VPN, Coreboot, and Mobile connectivity (e-sim) would hopefully become generally available.
Also, if you are a family or a group, moving in proximity, only one of you would need to carry the device(s)..