A good question.
A local answer.

Bring a picnic and water rather than depending on a cafe being open. Check the beach forecast and choose a shaded break if it is hot.

Keep travel days light and reserve full days for walks or local meals. One partner can enjoy cellar doors while the other focuses on scenery and lunch.

The route can work as a series of multi-night bases. Map the ferry and long inland return legs first; those fixed transfers matter more than adding another short city stay.

Check the forecast shortly before departure and bring a compact rain layer if showers are expected. You need not pack for every season in a single day.

Choose the region first: McLaren Vale, Barossa and the Adelaide Hills make different days. Then compare pickup point, group size, cellar-door time and whether lunch and tastings are included.

Plan d'Arenberg plus one or two nearby stops, with a lunch reservation between tastings. Driving and lingering outdoors take longer than a map of cellar doors suggests.

Choose a self-drive day only if someone is content to be the designated driver. Compare a small-group tour's pickup, group size and included tasting fees before assuming it will feel impersonal.

Map the direct drive first, then select a wine region that does not force a long backtrack. Book lunch and tasting appointments around your intended arrival time.

Group North Terrace sights together and give Glenelg or Hahndorf its own half-day. That avoids spending the week moving between distant stops.

For a larger trip, book any sport or performance seats together early. Keep a rest day and a wet-weather option rather than filling all eight days in advance.

At Wilpena Pound, choose a short ranger-led or signed walk before committing to a bigger hike. Carry water, sun protection and enough time to return in good light.

Break longer days with a proper lunch or short walk, and avoid arriving at an unfamiliar rural accommodation after dark. Check road alerts and fuel stops on each day's route.