Start some seeds. Start seeds of broccoli, cabbage, collards, brussels sprouts and Chinese cabbage. If you can find them as transplants, grab them. These love the cooler weather and will ripen up with much sweeter taste. However, because cabbage butterflies and harlequin bugs are rampant, they need to be covered up immediately with row cover or plant netting. Open the covers every few days to inspect plants, though. I had a few bug eggs get past my initial inspection, and they wreaked havoc, totally protected from birds and wasps by the netting.
Overseed the lawn. Late August is the best time to do this, so grass seeds have time to germinate and get some growth before the cold weather. Think about sun, shade, amount of foot traffic, and consult your local garden center (not the box store) for which grasses or mixes work best in your specific situation. Best to do this just before a gentle rain; oh, wait, we don't get those anymore.
Harvest garlic. Harvest any garlic that might still be left. Once leaves are dried and brown, there will be no more growth happening this season. Same with onions. Make sure to get all the little cloves that might have separated from the mother cluster. Inspect every clove to make sure there are no little maggots from the allium leaf miner lurking there. They look like little white worms, or small apple seeds if they've gone to the next stage of development. Soak everything in Listerine (generic is fine, but the yellow, not the blue) for an hour to kill germs, let dry, and store in a dry place until it's time to plant them in September or October.