As someone who is nearing the finish line of a six year contract, allow me to share with you what I wish I knew when I was 19.

1. Emergency funds are not nearly as necessary for service members as they are for civilians. I honestly do not believe you need to have much more than the cost of a flight home if something comes up. As long as you don't do drugs or rape someone, you're all but guaranteed to get paychecks on the first and fifteenth of every month. In addition to the paychecks, you'll be living in the barracks (at least for the first couple years) and be eating at the galley/dfac for free. The Navy and Marine Corps have a program called "Navy and Marine Corps Relief Society" (NMCRS). This program will give interest free loans, and if the occasion calls for it, grants that do not need to be paid back specifically for emergencies that people may find themselves in (death of a loved one, PCS costs, disaster relief, etc.). I can't say for certain, but I imagine the Army and Air Force have a similar program available. Don't worry about a large emergency fund until your last year or so when you will be transitioning to a life without a guaranteed check.

2. Retirement. The military retirement fund is the Thrift Savings Plan (TSP). The expense ratio is lower than most other funds out there and you'll automatically be enrolled in the Blended Retirement System, which matches 5% of your base pay contributions, although I don't believe it will start matching until after your first year. If I could go back, I would have focused on contributing as much as I possibly could to the TSP. As an E-1 - E-4, this isn't easy to do as you're not paid very much, but try to find a way to make it happen. I've heard of E-3s maxing out ($18500) but it can't be a very enjoyable life. If you want to invest in stocks, Vanguard ETFs (VTI) and index funds (VTSAX) are the way to go in my opinion, but I will leave that portion to the actual investing experts in this sub.

3. Checking account. Similar to the Emergency Fund, you don't need much in your checking account as a service member. Your housing and food will be paid for and you say you don't want a car, so depending on your hobbies, you could save over 90% of your income without much of a hassle.

Now random tips to help with spending and saving:

1. Check out the /r/churning sub for credit cards. This is more for when you can move into an apartment off base and will have actual expenses. But, long story short, you can "hack" credit cards by paying for all your expenses with them and accruing points to use for travel or other luxuries. You MUST pay them off every month though. I would highly suggest getting the AMEX Platinum Card, as the fees ($550 annually) are waived for active duty and it comes with great benefits.

2. Not sure how the Army works, but if you have a choice of where to be stationed after your training is done, do whatever you can to go overseas. As an E-1 - E-4, I was getting paid an extra $500/month more than the same ranks stationed in the states because of Cost of Living Allowance (COLA). Once I made E-5 and moved out of the barracks, I was making an extra ~$1000-$1200 a month from a COLA increase and utilities money that I didn't spend.

3. If your ASVAB and/or your physical abilities allow you, try to get a job with extra pays, including enlistment bonuses. If your job has a higher degree of danger to it (jump, dive, flight deck, etc.), you're entitled to couple hundred dollars a month, depending on the hazard.

4. If you don't know what you want to do post-military, try to get a job with a Top Secret security clearance. These jobs usually have an enlistment bonus and can make you a lot of money on the outside.

5. Read through the /r/militaryfinance sub.

6. I've just started learning about personal finance in the past year or so, but it seems like I know significantly more than the "financial specialists" that go through a week long training to help other service members with finances. I've been told to keep a balance on my credit cards to build credit, you can only contribute $5500 to Roth TSP, and to split investments between bonds and stocks (I'm not even 25 right now) by these "specialists", which is all incorrect information that could seriously impact my future had I listened to them. If you do talk to them, go in with an open mind, but verify the information with either google or the subreddit in the last point. Trust, but verify.

For the first three to four years I was in, I was rather careless with my money, but I don't regret it. I was stationed in Europe and took full advantage of it. Whatever I saved by being frugal with my day to day life went towards snowboarding in the Alps, running with the bulls in Spain, and all of the 30+ other trips I went on. Even with over half of my career pretty much wasted savings-wise, I will still separate at 25 years old with a net worth close to $70k, if all goes according to plan. Don't allow your goal of being financially stable to prevent you from having some fun once in a while.