1. Tour the island. Sometimes it's rainy in one area, and not in the other, and chances are, if you're driving around, you'll have a few lulls in the weather to get out and check out some sites (pose by the 'ROATAN' sign, sample jams at Marble Hill Farms, see the mangrove channels up by Oakridge and Jonesville)
2. Visit Carambola Botanical Gardens. Maybe not if it's teeming down, but a light drizzle or overcast day shouldn't deter from the natural beauty of the gardens, and there's a great view at the top
3. Take a dive course- you'll be spending some time in the classroom and doing confined water training, so the rain won't interfere with that, and when it's time for your dives, if it's choppy on one side of the island, it's usually flat on the other side, so you'll still get to dive (and you're getting wet anyway, so the rain won't matter)
4. Get creative and do some art. Sip and Dip Roatan offers paint nights at a few different spots around the island (we've done one at the hostel, it was lots of fun). Waves of Art has been hosting stained glass workshops.
5. Volunteer- the SOL Foundation has a community center in Sandy Bay, or help out at the Sand Castle Library or Care 4 Communities: all 3 have indoor facilities that you can help out in.
6. Enjoy some down time: read a book, catch up on your travel blog, organize photos, play a board game, do a puzzle
7. Practice making new cocktails :)