Everyone is correct with recommendations of USAA and NFCU, I have both. Your direct deposit (pay on the 1st and 15th) can go into separate accounts. I carry my NFCU debit card, and nothing for USAA (making it difficult to spend) this money gets moved into my Roth IRA and 529). This is a little advanced but I would get NFCU in boot camp and when you get to AIT set up USAA and set up a small allotment to get started saving.
TSP, early savings is best. I talked with some of my fellow officers and enlisted and few had taken advantage of switching funds to increase gains. We'll talk after AIT. Set this up in boot camp, even if one percent.
Don't buy a car! Get through AIT and ride in everyone's else's $500 a month freedom truck. If you want Ranger/SF you have a long training pipeline before you get to...
Deployment! Not if, when. Again we'll talk when this occurs. Highly recommend waiting until training is done, you get to your unit and you find out the deployment/work uo schedule. Sucks having a car/truck/motorcycle/boat/RV sit in the long term deployment lot as you make payments from farasfuckistan.
Don't get a wife/husband just yet. While you will be a solider they will be a kid a while longer. I could have saved thousands in plane tickets home to my hometown honey as well as the dear John letter during my second deployment. Tinder or okcupid at your duty station with the warning that girls around base will know your pay grade, understand your benefits better than you and maybe the Sergeant Majors daughter.
Take advantage of MWR trips, and hold off on a computer iPhones can do a lot. Take a college class, at least on during your enlistment, they give up to $4500? In tuition assistance, even better if you go the brick and motar community college down the street (real people to keep you human) vice AMU.
Talk to people and research all the advice you get, don't ask the E5 with a F250 diesel and 4 kids. Not sure the access to officers you'll have but look for 04/05 who likes like a family/man/woman they are not looking to impress others.
Enjoy it, you only do it once!