If there was anything different that you could have done throughout the course of your military career, what would that have been?

Ahhhh yes, the frustrating 'what would I do differently if I could go back in time' question! Well, I would have walked INTO the college campus ROTC office instead of walking by it....thereby earning my commission years earlier. But I like my college major (Business Management) and as far as my specialty (Combat Engineer) I have no significant complaints as I have found the adage to be true "you get what you put into it" when referring to your military career.

Simply stayed in.

This is a positive comment. One of the best innovations I saw in my time in the Army was the Family Support Group (FSG). When the relatives got together at the briefings, to support the troops ready for deployment, it was a real eye-opener into the struggles each family faced, and what I noticed was that the shared experience had a positive effect on how team members related to each other, and how the leadership gained a faster and deeper understanding of the morale issues facing the group.
Without giving away personal details, let me just say one broad brush example: I learned how important some of the quietest members of the team were to their handicapped relatives; and we later learned how much work it took by FSG members to provide support in their absence. Unless you have dealt with the handicapped population, you may not realize that about 13.5 percent of the US population is classified with some form of disability.
As a result of that experience, one gets to appreciate more the sacrifices that the families make to support their loved ones. I would hope that in the future the service would not cut the budget for the FSG's, not just because it helps the troops deployed at the moment and their families, but also because, when a veteran returns with a service-connected disability, there is a wider awareness of what the disabled have to go through, and that people can help make the life of a disabled veteran less difficult than it already is. from parking spaces to arranging transport to medical appointments. That would be my recommendation.

Airborne in my contract.

I would have skipped signing up for the National Guard and went Active Component from the get go. By the time I learned what i was missing I was too anchored in my civilian life to go for it.

Joined the Coast Guard.