Wondering which 8 data fields everyone uses on their Garmin.... there are so many.

I generally use 7 fields in the following order: Time, cadence, heart rate, speed, distance, grade, time of day. I suggest you try the Garmin user forums. lot's of good info and helpful users there:

https://forums.garmin.com/forumdisplay.php?f=20

Screen 1:
Ride time
Speed
Distance
Cadence
HR
HR Zone
Time of day
Avg 3s power

Sceen 2:
Lap time
Cadence
HR
Avg 3s power
Lap power

I use screen 1 for "normal" riding, and screen 2 for intervals. With only 5 data fields on screen 2, the top is lap time and it's really big, making it easier to read when I'm nearing the end of a 2-3 minute interval and having difficulty focusing on anything.