This can't be emphasized strongly enough. You need to be able to fix a flat by yourself. I strongly recommend that you find a more experienced cyclist and have him/her walk you through this. If you can't do that before the ride, go on the ride anyway, but get this squared away ASAP. Make sure the ride leader knows you can't fix the flat yourself...since this is a beginner's ride, he's probably prepared for that.

I don't know whether you can get a pump and/or CO2 on base or on the economy, but you need one of them for riding. You also need a floor pump to keep at home. Bike tires aren't like car tires - they're relatively porous, and need to be pumped up every couple of days.

AAFES isn't really good about stuff for road bikes. Many online retailers are comfortable with shipping to APO/FPO addresses, so plan on ordering the stuff you need that way.