Honestly,
if its just a weekend car, I dont see the point in taking everything out.
My old R33 was a weekend car then I basically brought it out for track use.
When at the track, I took everything out from the boot there, spare, tools, jack everything.
I had taken the back seats out so I didnt ruin them by having my semi's and track rims on them. When I sold the car, they went back in and were clean as and looked like no one had sat in there.
Unless your going to do something like Merli (see his GTR build thread in motorsport) thats where you want to remove everything, old wiring thats not needed, sound deadning, seats, seat belts etc etc otherwise you arent going to see good results from taking what you can for a road/weekend car.
The prev owner of my new car did this...
This was to fit the cage
Well, thats my thoughts and thats why I didnt do it!
Are you thinking of fitting a cage?
Another way to look at saving weight...
Remove aircon and heating
remove power steering
taking out drivers seat and putting in a lighter bucket seat
thats my 2.2 cents