I guess these first three are kind of limited scope improvents.
Fountain pens. Got me writing notes for work which has helped me stay more organized and on the ball and able to remember more. And with the right pen it makes note taking enjoyable.
Cast iron skillets have improved my enjoyment of cooking.
Portable jump starter has saved the day multiple times since I got it (me, friends, etc)
ADHD diagnosis late in life prompted by career-limiting struggles with a type-A boss. The diagnosis explained so many things about me, my behavior, my struggles in work and relationships, my self image, etc. Therapy helped develop better coping mechanisms and the meds help a lot with focus and motivation. All told, things are better with relationships and other areas of life, I turned around the boss's opinion and got my career back on track.
The big advantage over jumper cables (especially if you're a woman) is that you don't have to wait for anyone, or deal with a take-charge guy who has cables but doesn't really know how to use them and won't let you do it. Same reason I used to keep a wire clothes hanger in my bumper, back in the days when it was easy to lock yourself out of your car.
Oh I see you've dealt with a man like the guy who almost set my car on fire before I snatched the jumper cables and did it the right way myself. Alright, I'm sold. I'll get one before the first snow this year.
See a psych, not a GP. If necessary, get the rec. But don't trust the GP for this. Use them to push you to a psych. A lot of times, you don't even need a rec from a GP to see a psych.