Plant more flowers!
It's not too late to plant, there are lots of plants that will still flower (late season) this year. Nasturtiums and Calendula for example.
Plant summer veggies
If you fancy giving vegetable growing a go, you can buy small plants from your local garden centre. There will be a good selection to choose from - Peppers, Cucumbers, Tomatoes, Carrots and Cabbages.
Move your houseplants
Most houseplants can be placed outside between May and September. (timing varies around the country). Accustom your plants to the cooler temperatures and increased light intensity outside gradually before you move them out for the summer. Put the plants in a shady spot outside during the day and bring them back inside at night for one or two weeks first.