if you're staying in utila town (95% of visitors do), i highly recommend seeing the rest of the island: the town is the least picturesque part of the island.
make sure to visit water cay, pigeon cay and that whole south western area around jack neal beach, treasure beach, joes point and pinepoint (3 miles from town by boat). it looks like everyones ideal of the perfect caribbean get away, without the usual caribbean crowds. take a pack lunch with you, out there you'll find miles of empty beaches with just a handful of lovely rental homes on treasure beach that have a beautiful reef just feet from shore for snorkeling. also out there you'll also find utopia resort (the islands nicest hotel) and some beautiful uninhabited cays.
i would also recommend renting a kayak one day and paddling through the mangrove canal to rock harbor on the north side. take a packed lunch and make a day of it, you'll likely have the whole mile of beach to yourself, with its duck pond calm bay inside the reef for excellent snorkeling.
utila is really a tale of two islands: the town that occupies about 20% of the land mass and has 95% of the population and tourists and the other 80% of the island that has few inhabitants, a handful of beautiful rental homes and miles of unspoiled beaches with excellent snorkeling.
when locals or expats who live in town take a day off, these are the area's they go to get away for some relaxation and beautiful scenery.