The Fit is not the ideal vehicle for your requirements, but it's no turd in the big scheme of things.
A few days back I watched several dozen YouTube vids showing Czech lads driving truly POS, tiny little Russian or Eastern bloc cars. These are some of the crappiest cars ever manufactured. The Fit is an amazing polished diamond adventure vehicle compared to these steel heaps. The lads didn't snivel over the massive limitations. They loaded them up and drove them all over the world. It was inspiring and entertaining to watch.
Start with this vid. There are plenty more down the right column.
My old FJ60 Landcruiser had a 200 mile range. I never carried gas or ran out of gas. I planned stops more carefully. My current Escape has a 300 mile range. That feels like a plush luxury compared to the 200 on the FJ60.
In your unique situation I would get some sturdy tires. I like the idea of smaller steelies with a larger sidewall tire, but I'm guessing the selection is sparse. Pick your lines carefully when off pavement.
If you need some cheap roof rails, try a salvage lot and look for an older Escape or Explorer. They have a nice, universal style roof rail that you can rivnut to your existing roof. I dig those airline seat rails, but don't know if it is compatible with the front to rear curve of the roof line of your car.
The trailer hitch basket is a nice way of increasing capacity without messing up aerodynamics much. Easy on, easy off. Add some airbags to the rear if you get butt-sag.
Keep it simple. One thing at a time. Add or improve to mitigate actual, not perceived deficiencies.
Have fun, drive what you got!!