basic: shoulder strap, dust brush, zip lock for bad weather.
advanced: polarizer, ND gray filter, gradient gray, closeup filter, spare battery (especially if you can't keep from looking at the LCD screen), super light tripod (made one of old tent poles, gaffer tape and a mini desktop tripod, total 6 ounces)
lenses: 18-55 works for most things, a super wide maybe, telephoto only if you're into stalking animals or photos are the only reason you're out there.
consider the camera expendable like a pair of shoes and you're going to get great shots. If you're worried about scratches on it, leave it at home.