My peninsula is tiny, so I can't really do much with it, so I just threw some flowers on it. I also have my pumpkin patch there, but it could be moved once update v2.0 drops and I set up the new crops in the new farming area on my island and determine how much space I have left there.
The peninsula on my first island is a) the smallest, weirdest size and b) in the very top corner, near the cliffs. I just raised it to the same level as the cliff and ehh, it's a still a flower storage, even a year and a half later. A lot of wasted potential, having the peninsula I have. *sigh*
Second island's is thankfully larger, large enough for me to squeeze a villager's house on it.
I did some terraforming in the area to make a small cliff and placed a lighthouse on top of it. There is also a couple of iron chairs and the small round iron table outside the lighthouse, with blue and white flowers surrounding the area. I have a small waterfall down one side of the cliff that leads to a little pond at the bottom.
I do not have a picture on me but I have 3 surf boards, a beach ball, lifeguard chair and a pool. Right next to that area I have some rocks which I have a lighthouse on.
on my current island i'm still trying to figure out how to decorate it since i have quite a narrow variation of it, but on my previous island i made a little fishing area! i don't think i have any pics available atm but i just had a little bench, the fishing rod stand i think from the fishing tourney? and the squid drying rack with a few other things