Looking for Hawaii recommendations!!

Hi all,

I will be heading over to Hawaii in a few weeks and would really appreciate if anybody had any recommendations to share. It will be the first time that my girlfriend and I are visiting the islands, and we will definitely stay on Kauai and Oahu. So if you have tips to share I would be ever so grateful.

We are looking for awesome things to see / do and also nice places to eat.

One key question: we have 14 full days on our hand, so should we stick to these two islands and explore them in detail or would you say that we can squeeze in a third island? Which ones would you recommend in that case? :) Be aware that we are from Europe and not likely to visit Hawaii again in the foreseeable future as its just too far away.

Thanks a lot you guys!!