Not looking like a victim is the first and most important part... the smallest person can walk the darkest street at night without trouble if they walk like they aren't afraid of anything. Well, within reason.
Anyone considering pilfering your campsite will be encouraged if you don't look like the type who would give them any trouble. You don't need to look tough, you just need to have confidence. So if there are people around who you have concerns about, stand tall and openly appraise them; don't steal furtive glances or allow them to see you discretely hiding stuff away. In some cases it may be worth approaching them to talk - just ask how their trip is going etc. Don't ask if they know good swimming holes etc. because by letting them know you are out of your comfort zone you are taking that step towards looking like a victim. You might mention that you saw some dodgy types at your last camp stop and that they should be careful with their gear - shows them that you are awake and responsive to theiving. Say it in a manner that leaves no doubt that you'd have brained the dodgy types (but don't go overboard!).
Above all, don't worry too much about it, you are there to relax and enjoy yourself, and gear can be replaced.
As previously suggested, don't even think about having a weapon of any type unless you are prepared to use it (and are capable of doing so, know your limitations).
A mate has a small metal box with one of those black domes on it that hides surveillance cameras, an antenna, and a blinking red light. He made it from a Jaycar kit for about $20 in materials, and he leaves it on a table when he's out of camp - it would certainly make a tea leaf think twice about lifting anything...
