Anything about a doomed attempt to sail across the ocean in an unseaworthy boat which washes up on a deserted tropical island floats my storytime boat. My daughter enjoys this book a lot. She's still too young to understand the concept of friendship (she's 2.5yrs) so I dumb it down into more of an adventure book. However, I think there's definite value and comfort in the full story for those children who struggle to make friends.
I bought a used copy of Hangdog from our local library, and it was a favourite of my daughter when she was younger. I think I can still recite the first line "Hangdog was the lonliest dog in the world".