As you know, your precious plants will suffer in the heat so we have some tips to help them get through the heatwave and beyond:
Move potted plants into a shaded area and water them well. During heat waves, it's OK to keep pot saucers filled with water, as the plants can draw on that water over the day.
Temporary shelters made from shade cloth, or even a beach umbrella erected, will shield vulnerable plants can help them through the worst of the heatwave.
Water garden plants thoroughly the night before an expected hot day and apply a 3-5cm of mulch around the root zone of plants. Mulch is also beneficial for potted plants, as potted plants dry out faster than in-ground plants.