A lot. There are a ton of C-H bonds in triglycerides. Since I don't want to actually compute Hess' law, I'm just gonna assume 5 kg fat has the same energy as 5 kg CH4 - so there's 250,500 kJ released upon combustion of that 5 liter fat vessel.  We'll assume the car's combustion engine is 30% efficient, and converting to BTUs, we end up with about 72,000 BTUs. Now 1 million BTUs is about 8 gallons of gasoline, so we end up with about the energy required to move a car 30 miles. That said, the methane comparison isn't that ripe as fat is much more energy dense than methane.