When I was a kid, that question was so typical as to be expected, and planned for.
Every child knew that when school started again in the Fall, they were expected to have some sort of story.
It wasn't generally a difficult question, since most people DID take some sort of "summer vacation," going away somewhere to do those kinds of things that families couldn't do during the school year.
Travels to distant lands.
Visits to family.
The zoo, museums, ball games.
Fast forward to now, or to when my kids were growing up.
We didn't have summer vacations, as such.
At least the things we did during the summer only varied from the things we did the rest of the year in being season-related, but NOT fundamentally different from the KINDS of things we did during the other seasons.
Unschooling is, in a sense, a permanent "summer vacation." Without the summer part. And without the sense of being separate from, or different from, the rest of the time.
So to answer the question of what we do in the summer, I need to look at those annual things that are scheduled in the summer.
Swimming outdoors, or hanging out at Flatrocks.
The Farmers Market (which is almost all four seasons, but not quite).
Grilling, or various other types of outdoor cooking.
Summer rain and thunderstorms.
The annual fire department kid's day at the park, with fire engine rides and free balloons. (Yes, we still go.)
Fireflies and meteor showers.
Sweet corn, bought right from the farmer from a roadside stand with a coffee can for payments.
Baby animals, whether domestic or wild.
Movies- because the theaters are air conditioned!
Watching Drum Corps- whether live (not available often) or now, on the big screen, since DCI started offering that option.
This year, watching the olympics.
There are a million other things, of course, but most of them, we do all year. Reading, writing, playing games. Listening to music, dancing, taking pictures. Cooking, playing with the dog and cats, making plans. And the things on that list: visiting family, camping, the zoo, etc.
In short, what we do over the summer looks remarkably like what we do the rest of the time.