Sounds like a small generator isn't practical for doing a full recharge, but if you get stranded, a small generator might get you somewhere you can do a full recharge. I was thinking about those small generators that might fit in a trunk. Do those cars have any trunk space?
I agree with the comment that having a second car/truck that uses gas is probably more practical.
Still not practical.
My "small" 5kw gen is still ~150 lbs and 3x2x2.5 ft. You will have a hard time squeezing it into a Tesla. You can get small inverter generators that will physically fit in the car (Like a
Honda U3000) but you are still chasing your tail.
Numbers:
A generator small enough to fit in the car like I posted above will charge a Model S at approx 7 miles/hour. Honda says that EU3000 will run for "7.2 - 20 hours on a tank (3.4 gals) depending on load" The Charge rate we're using is 2.8 kw (98% of the gens rated load) so I'll round it off to 10 hrs on 3.4 gal. So .34gal/hr fuel use on the gen. Times 7 miles/hr charge rate is 20.5 MPG on the Tesla. With LONG breaks on the side of the road to "refuel".
Also, this plan involves carrying a generator and several cans of gasoline either in the back seat or trunk of a passenger car, which is generally contraindicated for safety reasons. (and might very well be suicidal in a Tesla, electrical discharge and recharging are known to be kinda ignition source producing.)
No, the answer in an evacuation is you leave the Tesla behind and take whatever your other car is. I strongly doubt that there's very many single car households out there that single car is a $100,000 EV.