According to my biochemistry professor the average 70 kg male has 420,000 kilojoules in energy reserves stored as fat. I am a little over 100 kg (and probably more stout than a "normal" male) so to keep the numbers easy I will say I weigh in at 105 kg which if you multiply 420000*1.5 you get 630,000 kJ. Now, one joule is equal to just over four calories. Seeing as how we're dealing with kilojoules and there are 1000 calories in one Calorie (aka kilocal or what you're used to reading on the nutrition facts) we can easily make that jump that there are just over four kJ in one Calorie. So, if I take 630,000 and divide by 4.184 I end up with 150,574 Calories of fuel reserves of just fat (fat is by far the largest reserve, though). Now, according to my undergrad physiology professor a person needs 100 Calories to run/walk/travel by foot for one mile. So, do I have 1,500 miles in me? Obviously not as a lot of this energy will be used for several other metabolic functions but it is interesting to think about.
In case you're curious about the rest of the stats for a 70 kg male-
170 kJ in glucose
2500 kJ in glycogen
100,000 kJ in protein (mostly from muscle)