Hi Leslie,
I have the same situation at my little beach cottage- scrub pines- nothing but roots, shade, and sand.
First- Check out the Northeast coastal forum for ideas from lots of sea side gardeners.
Her is what I have- low maintenance- I am only there on weekends. Window boxes- pack them with good soil, some absorbtion gel, and impatiens.
Next- Plants lots of different hostas for form and bones and in with the hosta- plant daylilies, astilbe, pulmonaria, and lilies- asiatic and oriental. You can plant impatiens in the ground also but you will need to water them. Also I have Aloha and Zephrine drohin( no thorns yay!) roses, and I am growing sweet autumn clematis and Hagley hybrid. Make sure you give every plant a head start with a mix of compost, and peat in each hole, and I try to add compost each fall. You can also add color with ornaments, bird houses on poles, buckets of annuals mixed in for color. Good luck...

Rugosa roses (beach roses) will bloom in an amazing amount of shade and they don't seem to notice they're planting in full sand. They will spread, over time, and form a thicket so give them room.