my rig is a haggard POS and I beat it like a stolen racecar, so that weighs heavily on my spares/tools carrying strategy... if you're nice to yours and/or it's in better shape than mine, you can probably get away with far less.
That being said, a lot of those things don't weigh much. My spares/tools *probably* weigh less than 200lbs, and if I cut out the crap that's optional or very rarely needed, I'm sure I could get it down to around 150 easy.
Oh yeah, I carry a spare thermostat, rad cap, thermostat gasket, radiator hoses, water pump, and water pump gasket after a bad experience with a radiator hose exploding due to a crummy pump and stuck thermostat two years ago. Forgot entirely about that stuff since it was behind the passenger seat.