A boardbag protects your board from from reckless luggage handlers and dads who pack the boot by shoving everything in and jamming the lid down as hard as they can. They can also make carrying them a lot easier.

Stretch Covers

These are nice cheap bags that just protect against minor stratches and scrapes. They usually don't have handles so it doesn't make carrying the board any easier. They are also good as a towel.

Back Pack Covers

Back pack covers are a good all round bag. Some have pockets for various things like fins and they have back pack straps so you can ride your bike with it... They are usually very strong and durable. About A$60.

Travel Covers

These are for the serious pro that takes 3+ boards overseas and stuff. They are well padded and they do everything. Make sure you have enough boards for the bag before you buy.