Normally I do the bar, and a very bro science version of progression adding quarters and plates until I am near 70%+ of my one rep max, then I use dimes&nickel jumps until I am satisfied.
Also when for whatever reason, mainly in competitions, conventional means of warm up and time aren't available, I will do the following:
Body Weight Squats
Standing Knee Raises
Arm Circles (for the rotator cuffs)
Light Resistance Band Stretching