I love this topic, oddly enough. Numbers are always important to me in sports for some reason.
HS Hoops: Frosh 34 for Ray Allen. Soph I believe I had 23, no explanation. Varsity I actually wanted 42 because of El-Amin (Jr yr in HS was 2000), I couldn't convince the guy who had it, and I got 33. That ended up being my favorite number to this day, so I sort of lucked out. I played one year in college, and in a twist of irony I couldn't convince 33 to give it up, so I had 42.
I played baseball my whole life, and I don't remember any numbers before junior in HS, when I didn't really have a number preference, and #7 was left. I took it, not fully realizing 7's greatness. I wore it two years on Varsity then 2 years in college, and every softball or baseball league I've been in since.
I also played a year of Frosh FB, #3 as a RB/QB/LB, but that didn't last long. I am too injury prone to play football. My body fell apart without a life of football.