Renting a boat and seeing Miami from the Oceanside is definitely something that I’d recommend. You get a really nice view of the skyline and the islands with the gorgeous mega mansions. There are plenty of sandbanks around where you can anchor up your boat and spend some time in the water.
On some days, you’ll find tons of people hanging around the sandbanks. Some are definitely pros and bring out tents and large umbrellas, which they set up in the water to provide shade while they chill out in the shallow water or on the boat, listening to music and having a few drinks.
When lunchtime comes around, you can head to a small cove by No Name Harbor in Bill Baggs Cape Florida State Park (Biscayne). Inside the cove there’s a restaurant called Boater’s Grill. The food is pretty good. Try the fish ceviche and yucca fries with cilantro sauce.