I would choose and maintain a sleep schedule, or at least a bedtime (I'm not sure whether infinite willpower would let me wake up without an alarm at a given time, and I find that having an alarm set messes up the quality of my sleep).

I would do more things that I enjoy while I do them, but fail to muster the activation energy to manage - going for walks in nice weather, cooking more complicated foods, etc.

My ability to do things very fast is currently hampered by my psychological need to multitask, take frequent and extended breaks, etc. With infinite willpower I would just do things very fast. I would take on more paid work.

I would probably learn to drive, if controlling my emotions at will meant that I could do it without shaking like a leaf for hours after the fact or freaking out so much that I become an actual road hazard.

I would presumably be able to stop eating things after noting that I am neither hungry nor enjoying them. (I'm improved at this relative to how I was when I was a kid but it sometimes happens anyway.)