Wheel weight - I've always been told that reducing rotating weight (wheels, tires, cranks, pedals, chain ring, etc) would reduce needed power for a given speed more than just reducing bike and/or rider weight the same amount. The thought was that since you are constantly doing small accelerations while riding that rotating weight was more "power expensive."
Seemed to make sense but there is not a lot of science to support that, especially since rotating weight helps maintain wheel momentum when power is removed, too.
GCN did a video of some simple tests that showed the gains were minimal -
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Anecdotally, though: when I flatted a GP5000 32mm on my rear wheel and decided I try one of my heavier Schwalbe Marathons which never flat, I could immediately feel the difference in getting started from dead stop. Could be psychological, 30% of people benefit from placebos, after all. But, I put back on the GP5000 after a few weeks!