James Lileks has an interesting account of attending his high school reunion in Fargo, ND, presumably his 30th. Among the things that Lileks mentions is that: "The band is too loud. Of course, the band is always too loud. Everywhere. It's what bands do: be too loud."
I attended only one HS reunion, my 5th, in 1975, in Rockford, IL. It was outside in a park, so the band was not too loud. The band, however, was Cheap Trick, which was pretty unusual for a reunion of perhaps 100 people (the band must have been fairly recently formed). Of course, we didn't pay too much attention to them, since talking to friends was the top priority. I remember going up after Cheap Trick's last set and talking to the drummer, Bun E. Carlos (aka Brad Carlson). We had been to a lot of the same concerts in Chicago in the 1960s (not together) and I told him that IMO the band (and his drumming in particular) compared very favorably with some of the groups we saw and used to talk about. He politely thanked me for the compliment.
At my HS in the late 1960s, our regular band for homecoming and senior prom was REO Speedwagon (a Univ. of IL band). At other dances, we had one of the two precursor bands of Cheap Trick. Today, many high schools have DJs.