Realistically I don't think your 1L summer is that important you really know nothing of any practical use at the end of 1L. However, some states do allow you to become certified to appear in court if you have finished first year and enroll in evidence during the summer. I did that and was certified and got to do a full jury trial while working for the public defender it was an enticing shoplifting case
not that interesting, but a good way to get some real trial experience. That was in California though and I know Louisiana is the only civil law state in the country and they may have very different rules regarding law student certification.
Many of my friends studied abroad and loved there experience I kind of regret not doing that personally. Once you graduate law school there will be no summers off and you can go to some pretty cool places through study abroad.
One thing to realize is that specialties do not really exist in law school. At any ABA school your first year will be Torts, Civil Procedure, Property, Contracts,Criminal Law, & LRW. Then you will also take Constitutional Law, Criminal Procedure in second year or perhaps in first year depends on how the individual school structure is, but that will be 30 required units most likley.
Then almost every school requires or highly suggests you take Corporations, Wills & Trusts, Evidence, Remedies, Marital-Community Property/Family Law whatever your state has, then Trial Advocacy. That makes up 2 years of law school then you might be able to fit a few maritime classes in which will be helpful, but it will not make you a specialist.
Also many people change the areas of practice they want I remember when I started IP law sounded great, but after one class I realized it was not for me.
Hope some of that is helpful good luck.
As for maritime law if that is what you want to do then working for a maritime law firm would be ideal. You might also want to intern JAG Coast Guard or JAG Navy that might help you out.