Well, we're back to that whole pointy ears thing, you have to have them(I'm rather fond of the Woochie brand latex ear-tips, available for about $10 at most costume shops, pick up spirit gum to attach them while you are there.) The second part is your Elf Stone, for a Sea Elf you will need a blue one. Makes sense, right? You can pick up flat backed fake jewels at any craft shop and most fabric stores, then use spirit gum to affix one to your forehead.
Moving on to clothing; Sea Elves most often wear woolen and knitted clothing. The women most often wear skirts on land, though not always. Both men and women are likely to layer their clothing, the winds off the sea can be cool even in summer and downright frigid in the winter months. Boots are the favored footwear for these elves as well; though during the summer sandals are more common. Like the Forest Elves, the Sea Elves often trade in dyes, and their clothes are more apt to reflect this. They are not garish, like the Rovers, but light colors, easily seen over a distance.
Sea Elves of both sexes most often wear their hair short, to keep it from getting caught by the wind on ship. They are rarely heavily tatooed, though often will have some design on hands or wrists (WATER-WASHABLE markers are good for this),facial tatoos such as their cousins often have are almost unknown.
Those that fight tend favor distance weapons such as bows and javalins, since most battles they face are ship to ship. Town guards will often have both swords and bows, however.
Jewelry tends to be close chokers and snug bracelets that are unlikely to get caught in rigging rather than loose chains and is worn by both men and women.