First, gather up your supplies (ignore the hole puncher, I ended using a box cutter):
You'll need a cereal bar sized box, paint for your life preservers, painter's tape, scissors, regular scotch or packing tape, 2x straws, a glue gun, a china marker, and a box cutter.
First, draw out your sailboat shape (step A) on the bottom half of the box on both sides. Cut out your sailboat shape (step B), but leave the bottom and the back half of the box attached (you can cut out the top flaps). Fold over the back half of the box (step C) and tape to the other side (step D).
Don't throw out your leftover cardboard pieces! You'll need them to make the sides of your sailboat; tape the top on and then cut them down to fit. Make sure all of the edges are taped down when you're done.
Cover your sailboat in painter's tape horizontally, not vertically and cut the edges (don't wrap the pieces around). I went over the lines where the tape pieces meet with the china marker to make it look more like "wooden" planks. Draw on and paint your life preservers, hopefully you have better art skills than I do! Once the paint is dry, outline it with the china marker, it'll look a lot better!!
Mark where you want your straws to go and make small holes with a box cutter to insert them. Glue them onto the sailboat so that stay standing up straight under the weight of the napkins.
When the glue is dry you can add your napkins (bonus: you get to use your everyday white napkins instead of having to buy fancy themed ones). All together it takes about 25min and costs nothing to make using things I already had lying around.