Of course, the very heavy ones would probably need a monopod or tripod. But how about heavy lenses used for situations where u need to be mobile and always ready(eg photojournalism)? A pro body with wide aperture standard zoom or telephoto zoom typically adds up to 2kg-2.5kg even without flash.
Using a strap worn over the neck is definitely not a good idea for obvious reasons. I think most people sling it over the shoulders. This method probably works to make it seem lighter to carry but I've tried it myself and I find it very inconvenient as it is always not in a ready-to-shoot position. You can use a backpack or a shoulder bag, but it's only good when you are not shooting or carrying equipment that you are not using at the point of time.
Would like to hear how you guys carry ur stuff around while shooting (equipment readily available)