You could get this with an extra battery which would give you about 10% of your range back. It is "portable".
https://www.earthtechproducts.com/zendure-superbase-v-power-v6400.html
Has anyone installed fog lights on the lower front grill area? I think that this would be better than ditch lights specifically for snow and fog. It would also be more aerodynamic.
Perhaps you could even use the EveryAmp accessory mount.
https://everyamp.com/shop/accessory-mount-r1t-r1s-2022/...
I am getting a Rivian in the month and plan on putting snow tires on in the winter. I currently have a Q7 and have another set of wheels. I swap each season. Discount tire does it for free. The extra set of wheels would allow you to go with a 20” and there are several available options.