there are some places that rent juke boxes with music from different eras google it to find out if you can do that in your area
Pick top TV shows and music from the year you graduation and use those as a theme. Or take your school mascot and dress it in clothes from the 90's vs. popular trends now.
Table top decorations for 80th birthday party for high school friends
Make sure everyone sits in their assigned seats from the initial seating arrangement.
Take classmate’s pictures from the yearbook and glue it to a cheap & tasty bottle of wine. Then, put the bottles on the wrong tables.
This is a fun way to get everyone talking!