In the web pages that follow, you will find descriptions of the eleven sea gods of Aegir's family, along with invocations, poetry, and short rituals for calling on them. I've also included links to journal entries by myself and others about working with the Nine Sisters, and suggestions for items to add to an altar. While there are various special items listed, simple items like bottles of seawater, sea salt, shells, and dried fish or fish-figurines are acceptable to any of the Nordic Sea Gods. Having the common Pagan problem of too many Gods to honor and too little shelf space, I built a "floating altar" for them, a mobile made of driftwood with branches for each sister, hung with glass sea floats, shells, ribbons, dried fishes, figurines of sea life, tiny wooden "buoys" with the names painted on them, small baskets with stones and shells from the shore, and anything else that called to me. To this day I can't go to the seashore without bringing them home a gift, whether from a seaside gift shop or from the beach itself.
If you don't live near the shore but would like to honor the sea gods, you could create a basin of seawater (mailed to you by coastal friends) and shells, or in a pinch some water and sea salt, although the Nine Sisters really prefer people who are willing to make an effort on their behalf. Bothering to find people to mail you actual objects from a seashore will get their attention better. Bothering to scrape together the money for a bus ticket and get yourself to the seashore, at least for a couple of days, is what they really want. Make the effort, if you want effort from them.
If what you want is for them to give you a favor, however, it will take more than a little salt water or even a vacation. For them to exert themselves for you, they want a fair exchange. They want you to show them that you value the oceans as much as they do. You could go to the ocean and pick up litter, or you could give something to one of the organizations listed here, or other organizations whose priority is to clean and save the oceans. If you want good, do good. Step up and help, and they'll help you.
For eating responsible seafood:
Monterey Bay Aquarium Seafood Watch