When you buy the full tank, the price may be close to the going rates locally, but that's not the gouge. The gouge is that you get no credit for whatever fuel remains in the tank when you return the car. Instead, you donate it to the rental company. So unless Avis, Hertz, or Enterprise is your favorite charity, this option is a nonstarter. And when a rental company fills the car, it typically charges two to three times the local price per gallon (or liter).
Scan a copy of your passport, any visas, and any debit/credit cards you’re traveling with. Password protect the documents, and email a copy of them to yourself and to a family member . If everything you own gets stolen, you can access them safely from your email account, take your copies to your embassy as proof that you’re who you say you are. Plus, you’ll be able to buy flights home and pay for accommodation with your debit cards to keep travelling/go home in an emergency.