Things that seemed really important to know when I was a kid but turned out to be totally irrelevant:

1. How to tie my shoes
2. How to ride a bike
3. How to write in cursive
4. How to skip (as opposed to gallop)
5. How to program in computer languages long since deceased (Pascal, Applesoft BASIC, LOGO)
   

Things that might have seemed unimportant at the time but that I'm glad I know:

1. How to snap my fingers
2. How to whistle
3. Being able to identify all the states of the U.S. on a map
4. Being able to do math without a calculator
5. Proper American English grammar and spelling (well, most of the time)
   
6. How to parallel park
7. Etiquette (again, most of the time)
8. How to touch type