I agree with Ron... the ferry ride is worth the trip and you really can't go wrong as long as you don't go to Shaw Island.
Both islands have plenty of unique restaurants with Northwest beers on tap. My personal favorite is Downriggers downtown Friday harbor. The chicken Gorgonzola salad is spectacular and so is the "too good to be true" which is clam chowder served in a sourdough bun next to a killer Caesar salad.
Renting bikes or kayaks can be done on both islands... Orcas Island has bike rental right at the ferry landing as does Friday harbor ( San Juan Island ).
I wouldn't bother trying to visit both islands... just visit one and visit it well.
Friday harbor and
Roche Harbor usually have live music almost every weekend. Great beer goes good with live music!
There are some cheaper places to stay in the islands if you are on a budget... here is a link to a few of them :
budget places to stay in the San Juan Islands If you'd rather pamper yourselves checkout this list of
hotels in the islands .
There are heaps of great places to picnic on both islands and enjoy romantic sunsets... there are grocery stores in Friday Harbor, Roche Harbor, and Eastsound. Or you can shop at Safeway in Anacortes before catching the ferry.
Try to arrive at least 45 minutes early for the ferry you want to catch.