1979. Went with my boyfriend and another couple (we were best friends dating best friends). As I recall, we had dinner beforehand, then went to a hall where there was live music. We had our picture take, too (I still have it downstairs.)
I wore a baby blue floor length dress with a white shawl...and because it was the 70s, my date also wore a light blue tux. (ugh.) Girls did get their hair and nails done, but no limos. We all drove and had our own cars.
Afterward, many of us went to a party at a hotel where one of the grads had gotten a suite of rooms. I remember the bath tub was full of ice and champagne! Drinking age was 18, and not at all strict for those under 18. Got home probably around 3ish, I think.