Saves having to worry about where to get calor gas if you're out of the country, although I hear that it's not as easy as it was in the uK now. Filling up with LPG is easy in many garages all over Europe. Go for it!
Without any doubt, it would be a solar panel. About 10 years ago, I attended my first THS and on the second night(sans solar panel) my battery gave up the ghost.
However, I enjoyed myself so much,shortly after, I invested in a solar system to prolong my enjoyment .
A month or two later, I signed up to 'Fun' and found myself on a wet and soggy Chester racecourse at Easter time.
Enjoyed myself again, but this time managed 4 nights without any battery problems.
The added benefit has been, meeting lots of lovely people.
Hopefully this Easter in Chester is dry