DH and I went for a week when I was pg with DC1. We hired bikes and it poured with rain for nearly the whole week. We still had fun, even though we were soaking wet and puffing most of the time (very hilly island).
There's an excellent, very posh, crazy golf course at the Oatlands Centre. We did a day trip to Herm and walked all the way round the island, which was lovely and relaxing. Castle Cornet was interesting. We also did some surfing and sea kayaking, which was fantastic.