polyurethane glue
Sometimes referred to as gorilla glue, however ®Gorilla Glue is a brand name not a type of glue (they have other types of glue as well).Polyurethane glue is waterproof and it expands (up to three times it's volume) as it dries. Some people swear by it, but I don't use it often, mainly because of the expansion.
While it makes it good for filling gaps, it also makes a real mess. It's sticky when wet and doesn't wash off easily. If you get it on your skin you pretty much have to wait for it to wear off over time. However, it's strong and good for bonding dissimilar materials as well as wood.