Welcome, matt --

You're on the right track, you just want to take it one step further maybe, and think in terms of alliances rather than individual carriers.

Since you have 13,000 miles on Delta already, you're a SkyMiles member. While Delta flights give you SkyMiles, there are other carriers that will also allow you to earn SkyMiles, so when you think in terms of a "back-up" airline, think first about another airline in the same SkyTeam alliance. (Or, since some feel Sky Team is the weakest alliance, think in terms of shifting all of your travel, where possible, to one of the stronger alliances such as Star Alliance.)

If you decide to stay with Delta and SkyTeam, that would mean Korean Air, Alitalia, and Air France as partners on which you can earn SkyMiles. Continental and Northwest are also supposed to be joining it soon, I understand, and KLM is not far behind.

Also, I'm not sure if this willl work for a few years, but American Express has a credit card that earns Delta SkyMiles, and comes with a nice bonus for sign-up. I don't know what the minimum age is, or whether one of your parents could "co-sign" the application with you.

Finally, we might be able to give you more specific advice if you were to tell us where you will be located, and where you're likely to be flying to. That sort of thing can make a lot of difference in what airline (and what alliance) you choose.