there is a surprising amount of gear one needs for general versatile walkaround photographic kit when you do not quite know what you will need
you should avoid taking too many options as this often results in poor image quality as you can't make your mind up - I often only take 2 or 3 lenses to reduce this issue
nevertheless you CAN carry ALL of the following in a fairly small backpack which won't break your back IF you buy Micro Four Thirds system
if you have a heavy, bulky Nikon or Canon digital SLR then get a sherpa or be really frugal about which lens you take and whether you will be taking a big tripod or not.
essential items to take in your camera bag
camera(s) with battery charged and memory card emptied
giving nicely saturated leaves in forest or garden scenes
giving deep blue skies
reducing reflections from glass and water
allowing wide aperture shots in bright sunlight if your camera only goes to 1/4000th sec and ISO 200
allowing wider aperture shots outdoors with fill-in flash without resorting to high speed sync flash
10x neutral density filter
great for allowing long exposures in daylight for lovely flowing water or blurred crowd shots
this will allow 1/4 sec f/2 at ISO 200 in bright sunlight and if you have a tripod or an Olympus OM-D E-M1, the exposure can be further prolonged by closing the aperture down
optionally, a Hoya R72 infrared filter if you are into infrared photography
0.6 ND gradient filter
great for avoiding blown highlights in skies and for giving more dramatic skies
for sunsets, also consider a reverse ND gradient filter