With high efficiency solar panels, you could conceivably get about 500W on the roof of a car. In most of the US you get 4-5 solar hours a day. So, ~2.5Kwh a day optimally, that's about 10 miles in model Y/3. We don't know F150 efficiency number yet, but it's likely half that initially, and half again when towing. Then again potentially larger solar area if you put a topper or something on. Bottom line, solar on an F150 MIGHT get you 5 miles a day.
The generator idea for occasional use is worth thinking about. The downsides being that, A) you'd need a large one to deliver power on a short trip, and B) you'd have to run it continuously to get a good charge. And C) generators run harder the bigger the load, so you might end up needing quite a bit of gas.
A common model is Honda's E2200, technically 2200 watts, but likely would only get 1500w of charging via one leg of 120v.
So that's 1.5KWH an hour. With the F150s estimated 200KWH battery, you're looking at 66 hours for half a "tank". 66/4hrs a gallon, puts you at 16.5 gallons of gas.
Obviously very back of the napkin, but running a small generator for 66 hrs over the course of a long weekend is doable, but not ideal.
A bigger 7000w generator, would output 240v and charge a lot faster but still consume a significant amount of gas. Say 6.5Kwh an hour, 100/6.5 ~ 15 hours. ~.75 gallon per hour ~= 12 gallons of gas for half a tank
edit: Not to mention the up front cost of $800-$5000 depending on how big/efficient/loud of a generator you want to run.