What to bring:
 
Backpack: (60-80L, depending on where and how long)
A good advice is to first fill the inside with a big plastic bag - this keeps everything inside dry even in tropical storms
I prefer to bring my own sleeping sheet (sewn as a bag), bring a good but compact/small medicine bag, sewing kit, knife + fork + spoon, chargers for batteries and for mobile phone, sunscreen, drinking cup, mosquito net and repellent, a few candles, and only the essential toiletry

Daypack:
Pocket camera (zoom is a must), spare battery for camera, pocket-knife, toilet paper, pens, notebook, mobile phone, Mag-lite + batteries, lighter/matches, pocket calculator.

Money belt (for inside trousers) is essential for valuables, but try spreading cash around in other pockets (preferably on inside of clothes), get a cheap looking watch and leave jewellery at home. 

Preparations: Some of us like the planning and find it to be a motivational factor when our jobs get stressful. Planning an exciting trip can take you through other hardships. Others want everything to be a surprise when they arrive. Still, showing up at the airport, just to be denied the trip due to lack of vaccinations or a passport that expires in less than six months is not very exciting. It is important to prepare a little! Before you go - do check what vaccinations are needed. Do check your passport (it should be valid at least six months after the end of your trip). It is also an idea to check out if ATM machines are readily available at your destination(s) or if you need traveller's cheques.

Behavior: Here are some guidelines from www.ethicaltraveler.com that one at least should give some thought to before setting off to new destinations.