Is there a AAA on the big island?

[TomK]

I looked into the international driving license in a bit more detail, and it turns out some European countries require and IDL in addition to you US driving license, although sometimes it depends on the rental company you use. Germany, Italy, Spain and Austria require an IDL although since the IDL isn't a true driving license, it's just a translation of your US one, you should carry both. Most other EU countries don't require and IDL and I that the UK and Ireland don't.

I can't vouch for the accuracy of this as I've never needed an IDL in the UK, France, Belgium, Ireland and the Netherlands which are the countries I've driven in, but it might just be safer to get one anyway.