There are lots of things you can do, besides a monopod and/or tripod...
Get a 5 or 6 foot length of 1/4 or 3/8 inch rope. Tie a 1/4 x 20 bolt in one end to screw into the tripod socket on your camera. Depending upon the bolt used, might need a washer on it so it can be snug up on the cord. Let the other end of the cord or rope drop to the ground and step on it so it's nice and taut when holding the camera in shooting position. Instant steadiness. I guarantee you can shoot a couple steps slower shutter speed using this trick. Plus you can easily coil up and put the cord/rope in a pocket.
If you don't already, learn to hold your gear right... I'm always surprised the weird ways people sometimes hold their SLRs. Left hand cradling the lens, right hand gripping the camera. Keep your elbows in tight against your torso. Stand with one foot slightly ahead of the other, feet approx. shoulder width apart. Exhale and don't inhale, right at the moment you trip the shutter. Try to time your shots between heartbeats. Press the shutter release... don't stab at it. It's a lot like sniper training, in fact.
5DII has a lot of mirror slap. Unless using mirror lockup, try to avoid shutter speeds around 1 to 1/30 sec, even on a tripod or monopod. Longer and shorter exposure, it's usually not a problem. But there's a zone of shutter speeds in between where the mirror can create enough vibration to cause some image blurring, even when the camera is on a tripod.
The higher the magnification, the more camera shake is a problem. That means both longer lenses and closer focusing macro are equally difficult to hold steady. Big lenses with large lens hoods are susceptible to breezes causing movement. At times it's better to remove the lens hood. Other times I've hung a camera bag from the tripod, adding weight to help steady it, and laid a beanbag on top of the camera/lens. Carbon fiber and wooden tripods/monopods are much better absorbing vibrations than metal tripods/monopods, too.
Buy stabilized lenses. They help, but you have to give the IS a moment to do it's thing. Thanks to IS being in the lens itself, you can see it working in the viewfinder.
Sometimes it can help to simply take extra shots. Switch your camera to it's highest frame per second continuous shooting rate and take 3 to 6 frames, instead of a single shot... One of the frames is likely to be steady and sharp enough.
And, yes, a battery grip helps a lot. The extra mass helps balance the camera even better than a big old flash in the hotshoe. When shooting vertical/portrait orientation, it also helps to have the seconday grip and controls to use, so that your right hand isn't oddlly turned to hold the camera by it's main grip.
Speaking of flashes... a flash bracket and off camera shoe cord can help with hand-holding, too. Though shooting with flash itself also is a big help. Most of the time the flash exposure, if it's "full flash", i.e. your primary light source, is equal to a shutter speed about 1/720 or faster, no matter where your camera's shutter speed is set. However, this doesn't work if using fill flash, i.e. mixed with ambient light. Then at least part of the exposure is dictated by the camera's shutter speed.
Sometimes it's just necessary to keep shutter speeds up. Canon themselves have noted that the 18MP APS-C cameras seem to be more susceptible to camera shake than cameras with less crowded sensors. They recommend trying to keep shutter speeds a little higher than with lower resolution cameras. (A 7D, 60D, or any of the 18MP Rebels have over twice as many pixel sites per square mm as the 5DII has.)
Practice, practice, practice... we all tend to get better at hand holding our shots, the more we do it.