What, if anything, do other E3s of any other branches do for money as side jobs?

Well Joe C, I'm an active, retired, disabled, Vietnam Vet, SGT E5, finacially set. I think I can help you, so do you have a cell phone and a lap top computer ?

I've only seen one junior enlisted member with a side job. She delivered pizzas.
I believe you must get the "permission" from your command, but I'm not 100% certain on that.

I am new to the Military, Army National Guard.. so, I cannot speak for other branches, but other Soldiers in my RSP unit, work similar Civilian Jobs that mirror their MOS.. I work as a Hospice Nursing Assistant, soon to be a Nurse.. I am not sure if that helps.

Back in the day, '86 I think, I was a good radio mechanic. I made money on the side working for a local pawn shop installing car stereos and driving soldiers to the air port who were traveling home on leave. I also used to hustle in the field. I had to take equipment to the rear for repairs so I had a 50 cal. ammo can I'd pack with ice and cold Pepsi's. I'd get $5 a can for a Pepsi at Ft. Bliss from the tankers almost all day long. We also used to trade anything for anything. Bullets for bread and apples, commo parts for vehicles parts, Class A uniform and TA-50 gear, Batteries for flashlights, smokes for candy whatever. A resourceful guy can supplement his income and live well.

That was cold! I when I was an E-3 I drove a bare-bones pickup, while stationed at Oakland Army Base I worked as a hotel security guard, stock boy at a grocery store and a night club bouncer. Not all at the same time but Ca was crazy expensive in the 80's.

fortunately for me, as a young Lance Corporal in the Marine Corps, they stationed me in 29 Palms, in the middle of no where, without transportation , or friends, at the time, so I spent a lot of time at the gym, and hiking the desert, so I wound up saving most of my money for the year and a half I was there, until I went to my next duty station as a corporal.

I recommend not having a side job. If you are going to do it. Get a job that is flexible with availability and hours. Lowes and Home Depot work well with Guard and Reserve troops. Different situation with Active Duty personnel. If you're active, be clear with your manager on what's going on with your military obligations and always remember your service obligations come first.

As an E3 in the coast guard in Boston back in 99 I worked at a bar as a door guy and a mc Donald's as time permitted as they had a flexible schedule. Made 12 an hour then at mcd's as a fry cook. In Alaska I made some coin working at the local hardware store/gun store

As a young USAF Airman with a wife/child I delivered newspapers for extra income. If it were now I might think about Uber or Lyft for additional income. The main consideration is your schedule for your primary duty.

I taught karate after hours throughout a 21 year career, at one time I was making more doing that than my E7 paycheck brought in.