1. Snorkeling: if you've got your own snorkel gear, this is hours of free entertainment! The reef is just a 200 meter swim out from shore, even closer in some areas, and there's a huge diversity of marine life and healthy coral reefs. If you don't have your own snorkel gear, you could purchase a set if you're staying awhile, or rent out from the hostel for $5/day
2. Rope Swing in West End: this is a favourite activity of many visitors and locals, including my kids. Swim out to the sailboat at Half Moon Bay in West End, and enjoy playing on the rope swing attached to its mast.
3. Beach time: All beaches are public access, if you can get to them without going through someone's private property. West Bay is the most well-known beach on the island, but there's also Half Moon Bay, Sandy Bay, or trek all the way up east to secluded Camp Bay (it's pretty far- you can try hitching a ride if you're trying to save on cash, or team up with some other travelers to split on the cost of a rental car)
4. Volunteering: there's nothing like helping others to realize how blessed your life is! There are various volunteer opportunities around the island, even if you only have a day or two to donate (contact Roatan Because We Care, Sol Foundation, Care for Communities or R Church for short-term volunteer options).
5. Hammock time: a shady spot, hammock, cold drink and a book is a winning combination. Relax and enjoy island life at its best.