What three skills will be the most important in your opinion to help you through the first adventure as a suggestion for a gnome summoner, have not decided yet if becoming a siege weapon especialist or a cook...
Siege weapons are not involved at all in the first adventure, and frankly aren't terribly useful for PCs in general. Too many feats to use, too little damage, and not much of a point when you can easily and completely disable enemy ships with magic.
If you decide to be a cook, I'd say the three most important skills would be Diplomacy, Profession (Cook), and Perception, as well as a single rank in Profession (Sailor) eventually (maybe Profession (Fisherman) too). There are lots of other skills that could be helpful, such as Acrobatics, Climb, Stealth, Survival, and Swim, but with so few skill points and few class skills you probably don't want to be spreading yourself too thin.
I'd say the most important three (in order) for the first adventure are:
Swim
Climb
Profession (Sailor)
In order of importance, I'd say:
Diplomacy
Swim
Profession(Sailor)
For the last, it's possible that you can get away with a single rank, but you should take it at first level. After that, you may find something like Perception more useful.
Thanks guys!
Between Profession (Sailor) & Profession (Cook) I think if he decides to be a cook should he get Profession (Cook) first so he can get the +2 gnome racial bonus? What do you think?
If you plan to be a cook, the Profession (Sailor) is less important for the first few levels I think.
I's still put ranks in it eventually. At least one, as Tem suggested, but yeah, you could totally manage with just Profession (Cook) at first, (just make sure to not wait too long before taking Profession [sailor]).