The Jamboree site is generally a safe place, with IST working dedicated jobs as security to ensure visitors are only allowed to certain parts of the site. Saying that, you should be cautious of your belongings and avoid leaving them alone on display. Things like solar panels can indicate you've left something valuable attached. It is not unheard of for tents to be entered by scouts from less fortunate countries so it is best to carry anything you absolutely do not want to loose.