Campbell,
You wont find any “heavy parts” left on a race car but you can find many places to remove 1,2 or even 3 lbs and it all adds up very fast. Well maybe not very fast but it does add up.
As far as the bumpers unfortunately you have to keep them, and I have found that they do come in handy at times

My 2 biggest weight loss items will be the spare tire securely mounted in the truck, and the spare tire hanging over my belt.

Matt bal