This has been a difficult one to calculate as:
1. The guage is innacessible due to the way the tank has to be fitted
2. The guages appear wildly innacurrate
3. Whenever i fill up with vehicle gas - this fills the leisure gas tank.....
So- having the need to empty the tank completely (long story) I have been running the following continuously:
2 burner hob - both on full
Propex heating - on hot
Electrolux Fridge - on gas
I have managed 11 hours continuous use - generally heating the atmosphere on the warmest day so far. The hobs were still going strong - but the guage reads empty.
So - if you go camping with someone who insists on sitting in an oven - but wants continuous hot tea with cold milk - you can go away for 11 hours

Or more sensibly - you get a hellovalotof leisure for £5 (filling cost of 10 litres)
Hope this is useful to someone.