Well how old are you? Can it be sexy/showy? Are you going to model swimsuits or just summery clothing? here are a few outfit ideas;
I saw an article the other day about this, let me check my history real fast and I will get back with the link
Look at other shoots and see what they used and what you have in your wardrobe. I guess neither of you wants to spend money on the outfits. A shorts sexy dress in the sea can be very good if you do not mind getting it wet. Partly it depends on where the shoot is, very public or secluded. It also depends on how sexy and risky you want to go.
Sure you are.................
Bathing suit, a button up that compliments the swim suit, some blue jean shorts or if you find any then a colorful pair would be cute and then to top it off add your favorite pair of stylish sandals head wraps and floral headbands also known as flower headbands would look very pretty