Yeah you can get full units that fit to your car but hand helds are probably better and easier for this type of thing. I got 4 from dick smith for about $150 or something. I think single is under $50.
Just make sure its UHF band and not AM, or it will be useless to you.
On the the question about the police. I have been on several cruises where they meet at the meet points. Never seen them issue anything. They normally drive around, talk to a few people, have a look around to make sure no one is doing anything silly. As long as its all good, they will leave with no problems at all. Unfortuantly as soon as 1 person does something stupid, they get a bit upset. I think hillarys was different due to the large amount of fools/racecar drivers if you know what i mean.