Even with the KIT lense you should get better results then most pocket cameras - depending on the subjects, shooting conditons, your skill and creative ambitions. If you're thinkinng of a lense to add to your KIT - then that is probably a somewhat personal consideration. IMHO you must already have some idea of how wide or narrow a perspective you weigh heavily with. Or - you may or may not be critical about image perfection. When I started usig my digital rebel I was quite happy with just the KIT lense. Then I added a 28-200 canon zoom and blissfully shot most shots with it. Only a year later were my suspicians cofirmed that the 28-200 was a bit of a dog. It was unsharp and sort of a poor performer all around. BUT - I was otherwise happy with the power of the DSLR body.
Then I swapped bodies (Replaced the Drebel with a 10D) and sold the 28-200 in favor of a Tamaron 18-200. This was curiously tack sharp at times - while at other times it actually missed focusing! I figure it was a design or software interface issue somehow since it was not a Canon lense. So at this point I was fed up with the underperforming Canon 28-200 and odd performing Tamaro 18-200 and I decided on a retail purchased Canon 70-300 IS f4-5.6 zoom. The 70-300 is a woderful lense and it seems to rival my comparisons against a 70-200 f4 L lense... plus the reviews peg it as a close performer on a 1.6 sensor. So I'm quite happy.
Now I am in the market for a 24-85 or a 28-105... depending on which comes up 1st as a bargain on Ebay or whether I get emotional about one or the other. For now I squeek by on the 70-300 and a Canon 20-35. I am not ready to plop down the big bucks for L lenses where I have difficulty seeig a difference or reading measured test results that certify the performance gains. Yeah... I know the L lenses are weather sealed, fit and function better then the consumer grade line - but I am really happy with the value and performance of the consumer line lenses.
If I were workig with a full frame sensor then I have no doubt that L lenses would be preferred if not required. I can see differences = but not so much when we are using the sweet spot of a lense in the 1.6 sensor DSLRs. Gotta love the design advantages there!
So... if you're thinking about another lense... maybe you could BORROW a lense from a Canon pal for the cruise. That might give you some experience with another focal range without the up frot expense. Either that or read about lenses here, on Fred Miranda and PhotoZone... and pick something to buy. I do believe though that you should NOT rush a decision. In thoery you will have the lennse for some time.... and resellig a used lense on Eay is a bit of a hassel.
Hope this helped more than confused you!
Cheers!