A:  Too bad the temperature will be that cool, but in the spirit of the cruise I would pack some fun and flirty outfits.  A cruise is a time to play, so I would recommend a couple of fun dresses to throw into the mix with your jeans.  As for what to wear with your jeans, you can always take your outfit up a notch by throwing a wrap around yourself or adding a cute short sleeved jacket to coordinate with your jeans–and the dresses. 

Here are a few dresses to get you started:
Free People ‘La Isla’ Embroidered Voile Dress | $118 at Nordstrom
Twisted Heart ‘Bianca’ Hooded Terry Dress | $143 at Nordstrom
BCBGMAXAZRIA Flutter Sleeve Knit Dress | $178 at Nordstrom
(Pictured) Diane von Furstenberg ‘Reno’ Silk Damask Shift Dress | $325 at Nordstrom
Theory ‘Azuri - Acute’ Printed Dress | $455 at Nordstrom

And a few separates you might find cruise-worthy:
BB Dakota ‘Evie’ Jacket (in White) | $44 at Nordstrom
Free People ‘Indian Princess’ Racerback Top | $98 at Nordstrom

The dresses I am recommending would look pretty with heels or flats, and the white Free People blouse with jeans would show off any tan you may get.  During the day, jeans or walking shorts with a cute tee or blouse would serve you well.  And if you invest in a short sleeve jacket (like the BB Dakota one), you’ll be covered–even in 60 degree temperatures.   Have a fun filled three days in Mexico!