My $.02 to add to Guns...
Warfighting spirit - Yea. Hell yea. The USAF is shrinking FAST (will be the smallest in size EVER within the next year or two) and that means that every single career field has the potential to end up in combat either in their career field, or as an "augmentee" on loan to whoever needs bodies that week. That means whenever their deployment cycle comes up, even a finance NCO may find him/herself in the middle of the desert wearing full kit wondering when his truck is going to explode (for example).
Jobs - Lots of requirements for security forces, but frankly some of the least happy airmen in the force are in SF. The job although absolutely critical, doesn't attract the best and the brightest because the job can be mind-numbingly boring. It's a commonly tossed around factoid that the base police blotter is usually full of SF troops getting in trouble... That's not really a reflection of the troops as much as it is a reflection on the nature of their job. Sit post for 10 hours and the desire to get out and raise some hell can be incredibly strong.
I'd actually suggest considering aircraft maintenance. Those guys work their butts off but they see real tangible results from their efforts. MX units often have very high morale (usually tied to the morale of the flying unit and spirit of their group commanders) and there is real opportunity to advance and excel. Regardless of career field however, the real determining factor of how well they do both in the service and after they get out is how much time and effort they put into self improvement. I've known master sergeants who retired with PhDs or multiple masters degrees, and I've known 20 year staff sergeants who retired without knowing anything except how to do the same primary job they did for the last 20 years. Both retired after AF careers, but one was obviously better set up for life outside the USAF.
Do your job and fart around off duty, and you're not going to move up either in or out of the military. Keep trying to improve yourself, and you'll be rewarded both in and out of the service. As an example, yea a military maintainer WOULD need certain certifications to be able to work as a civilian maintenance tech, but they can either work to get those certifications while they're still in the military or they will quite often find that civilian employers will either sponsor them to get the required certifications or offer guaranteed jobs as soon as they get certified. Either way, a military service record and honorable discharge is generally considered at least as good as the same number of years of experience in an equivalent civilian field, PLUS NCOs will be credited with leadership or managerial experience because almost every NCO in the military is going to get some sort of leadership experience in their everyday jobs.
As for those prior military currently doing manual labor, that's really a mystery to me. I won't pass judgement on them because I know nothing about their situations however that is a pretty unusual fate for prior military who didn't leave the service because of some sort of problem... Maybe they're unlucky or maybe they're not looking for the right jobs in the right places, but that is really strange. With US unemployment numbers near historical lows right now, there are tons of companies looking for people with the exact qualifications that almost anyone with military service will have.
Maybe they need to check to see if they can still get help from the military transition assistance program, because that service offers job hunting assistance to every military member when they get out. Maybe they didn't take advantage of the program when they left...