What job can you get on the civilian side after being a combat engineer in the Army?

Aside from the most obvious one, working with demolitions (more of it in the civilian work than you may think), 12B''s come out with basic carpentry and construction skills, wheeled and tracked vehicle maintenance skills, and often licensed that would be the equivalent of Class B CDL and often with a Hazmat rating. As a Combat Engineer Platoon and Company Commander, I was required here to carry a Hazmat First Responder rating, as did the Platoon Sergeants.
What's probably more important, that 12B has shown that he has the desire and life skills to be successful since he has survived a tour in the Army. A lot of employers across the Construction trades look seriously at Prior Service people since they are used to maintaining a schedule and being on time, plus being part of a team.

Speaking just for me, I worked in several construction type jobs after leaving the military. Ended up getting NCCCO certifications as a Crne Operator and that’s what I still do and am loving it.
Tuition was paid through my VA education benefits and the starting pay for crane and heavy junk operators I a heck of a lot higher than the labor side of the house. Average start paying for HE is between $15 & $20 per hr. and $20 & $25 for cranes. Experience gets pay increases pretty quickly if you don’t mind travel.
That’s definitely something to check into.
Get back to me with any questions and I’ll be glad to answer the best I can.

Uh, teacher in a public high school???

I pulled a lowboy trailer in Vietnam and hauled the heavy equipment all over.
I drove semi over the road as a civilian. Also drove dump trucks in the army
and drove dump trucks after the army also.

When I got out, I went to college and initially worked as a builder of home speaker systems , got into security solutions after a couple years and rapidly advanced through the ranks , from 1st line uniformed Supervisor to Sr. Executive at national level, if you posses the skill sets, work ethic, comittment and have the ability to lead , be led, execute and continuously learn, you can be successful in any field you choose, don't be afraid to take a entry level position with a GOOD organization and apply yourself, the top performers always standout. There are a number of combat arms vets high places!

Beer sales and construction

None

Custodian lol. All jokes aside you can do a private contract while your secret security clearance is active still. If you want to stay federal if you join FBI and become an agent for 5 years, after those 5 years as a regular agent and have eod or combat engineer experience in the field for 3 years or more you can be eligible for their EOD school. College may not be necessary either.

Anything you put your mind to.

Basically from what I see is equipment operator, or construction inspection that will lead to construction management if you want to go that route. There are tons of specialized training that is relatively short that employers will send you to... then there is always demolition, something we all like to do. I would take advantage of any college work that's credit toward an engineering degree in civil or structural engineering if you lean in that direction. That's a difficult path when your young and running around all over the world having a good time. :) It's a bit easier now with online schools than it was in my day.