Need somewhere to have a dip on a hot day? Sick of the crowds at Bondi? Drop in to Redleaf pool (harbour beach) for a free dip. It's surrounded by a boardwalk to keep you safe from anything in the harbour (it also gives you something to jump into the water from) and has this great Kiosk to keep you cool.
They sell ice creams, drinks and general snacks (my personal favourite is the good-old Frosty Fruit). Although there's usually plenty of people and they're the only place to get supplies, they're not outrageously expensive. In fact, really reasonably priced.
Also close by is the Woollahra council chambers and Woollahra public library. Why not drop in to the library and grab a book, get some food and drinks from the kiosk and spend the day lying by the Harbour on the sand. I've spend many days down here and have to admit that it's almost better than the beach...almost.