Elukka

Parachute -- Pod -- Decoupler -- 4 x fuel tank -- Liquid engine -- Decoupler (to get around the weird stuck-on-pad bug) Single stage to orbit with plenty of fuel left to deorbit. If you really wanted to stretch it, 3 fuel tanks is probably doable if you pilot it ideally. I don't think it's possible to get much more minimal than this.

So... You don't need a complicated rocket to reach a stable orbit. That is the only stage, nothing was jettisoned, not even SRBs. Well, there's a bug where it gets stuck on the pad so I added a decoupler to the bottom and left it on the pad. Plenty of fuel left to adjust orbits and deorbit, too.

OBV(H)-1 (I make stupid acronyms because I can't come up with a name) is my first heavy rocket. On the first flight it inserted the upper stage with an almost full tank of fuel into an orbit with an apogee of 600 kilometers and perigee of 380 km.