Can you attend the sandbar without getting there by boat or jet ski? Is there a part where you can walk on land onto the water?

Nope... no walking. However, you could rent a Kayak @ Oleta Park

No, the adjacent parks are a good place to hang.

The only way to the sandbar is kayak jetski or boat or a friend with a boat you can always rent a kayak from oleta state park

Nope.

Just jump in from the gas station!

Buy your own kayak on Amazon is just $ 100. Cheaper then rent it.