Well, first, get your commission, work hard in fight school, then be the best NFO you can be. The "jobs for ex-NFO" thing has been hit on in other threads, so do a search and come back, though the gist is that you'll be an experienced officer and capable of anything on the outside that requires leadership and management ability.
As far as degree, do whatever you're interested in for undergrad, i.e. if you're passionate about something, you'll probably do better in it. For grad degrees, DON'T get an aviation degree (how do you get a "minor" postgrad anyway?). It's pointless. You'll have all the aviation experience you'll ever want, and a degree in that will just pigeonhole yourself from potential employers. Law enforcement? It's a dubious even as an undergrad degree, to be honest (phys ed was taken?), and LE above the local level won't care. Off-duty cops get that degree to advance their careers--federal law enforcement wants critical languages, accounting, computer skills, etc.
Air marshall? That's got to be the worst job in law enforcement. Riding coach, NOT drinking, and not doing anything, ever? A LOT of those guys are using it as a steppingstone to an 1811-coded criminal investigator gig at another agency. Those run the gamut, and there are better websites than this to get the gouge.
Lastly, you might just decide that you like the service. Almost everyone joins thinking they'll leave, then a good portion of them stay the duration.
