I read through most of the responses, but I dont feel like quoting everyone. So I'll sum up as much as i can.
:: If he asked you for your name and date of birth, or made you present a photo id, he ran you for a records check. Standard procedure every time they talk to anybody suspected of anything. Ever wonder what the cop does when you get pulled for speeding and he takes your DL back to his car? He runs a records check on your license plate to check the car's owner and then runs a check on your DL to check you. A lot of times, people might be driving a card that their parents own. For example, my vehicle is registered in my mom's name because that way it gets cheaper insurance. So if they run a records check and see the car is not stolen and the vehicle owner is not wanted, that's great. But if the driver does not own the vehicle, that says nothing about the driver's status. So they run your DL to make sure there are no warents ALREADY outstanding. When he called over the radio it was to do a records check, not create a new warrant.
:: At 3 in the morning, about the only people out on the road (walking or driving) are cops, and people up to no good. So when a cop sees a person at 3 in the morning walking by themself, he wants to make sure they arent getting ready to commit a crime or walking away from one already commited. There's no law saying a cop can not stop you and talk to you. As far as the alcohol, more than likely he could smell it on you. I work for the Student Police at my university and we provide a safety/security escort for anybody going to and from campus by using vans owned by the police department. I've had plenty of people get into my van that, though they acted just fine, I could easily smell the booze on them. And I'm not even trained to detect the smell of alcohol. Officers get trained on what to look for (or smell for, in this case). He walked up to you (not illegal), smelled the alcohol on you, and wanted to see if you had any more with you. You said no, so he didnt search. Then he called his dispatch to run a records check on you, which he would have done no matter if you consented to a search or not. Note that the more cooperative you are with the police, the more cooperative they are with you. If you say "look, I'll admit I had a couple drinks, but I needed to get home because of some reason, and I decided to walk so as not to drive under the influence", then there's a better chance he'll let you off with a warning if you have a clean record. Now, that in mind, you have every right to refuse a search. But you turned around and gave consent, so he proceeded to search. Nothing wrong there.
:: Breathalyzer...different states have different rules. Generally speaking, it is a criminal offense to refuse a breathalyzer test. In South Carolina, you may refuse to take the test, but you can lose your driver's license for up to 90 days. Whether the penalty for refusing a test while on foot and not in a car is different, I dont know. But more than likely refusing the test is going to be another penalty, on top of the MIP citation if they were to find a container in your possesion.
Long-short: Everything the officer did was on the up and up. SiliconC was not in a vehcile, so the officer did not need probably cause to perform a traffic stop. The officer doesn't need probably cause to stop and talk to you. In talking to SC, he probably could smell the alcohol. This gave him probable cause to ask to perform a breathalyzer test. SC accepted the test and blew an illegal limit.
"I know I was "breaking the law" by partaking in alcoholic beverages while underage, but honestly, what problems was I causing? In the arguement we had, the police officers couldn't even come up with a reason, but still gave me the damn minor. I oppose much of the United States' drug laws, but this just seems ridiculous. If I was causing a problem, I could totally understand them stopping me, but me walking home by myself doing nothing wrong? "
You broke the law. It doesn't matter if you were causing a problem or stumbling drunk. You broke the law and were fined for it. "Doing nothing wrong" is not a correct statement. You were a minor in posession of alcohol, and you were also intoxicated in public, which is a totally seperate charge you could have been fined for. The breathalyzer test showed that you were intoxicated, and you were walking around in public. But as far as MIP is concerned, you did something wrong in the eyes of the law. If you didnt want to get fined, you should have either not drank at all, or stayed at your friend's place over night.