For those visitors on holiday or stranded another way to make the money last longer.
This week is National State park week and all 392 National parks are offering free admission for the week 17-25th April

[website link edited]

If the link isnt allowed if you google national state park week you should find it.
Most of the State parks have picnic areas with bbqs so youu can take your food along.

We went to the Castillo De San Marcos National Monument on our last trip (had to pay though) and it was very interesting.