Concentrate on Seo first, get tons of content and organic positioning on google etc. Atleast then profit is profit and not eaten away by PPC (not that there's anything wrong with PPC!).
Definatly get onto sweetpete about Thomson, good chance of making a fair bit of money on a 6% commission.
Have you thought about promoting Easy Cruise?.... Its marketed for a younger demographic that would be more willing to book online. Like what was said before older people go on traditional cruises and these people will always tend to favor phone booking or via their travel agent even if they are starting to do their primary research online.
I dont know if Stelios runs an affiliate scheme for Easy Cruise but im sure you could find a nice section of your site to promote them if he does. Would seem like the perfect opportunity to get some web commissions in!
Also there are drink cruises lasting for a day or night in the UK, just Google party boat and you should get something. Exact same demographic as Easy Cruise and you could sell that. I would try and keep the two sections to your site roughly separate as older people may be put off if they think your selling young 18-30 type cruises and visa versa. Perhaps brand the two entities differently with a base colour change so that people know which part of the site they are on.