I customized my Stormtrooper Commander, I will call him Lieutenant Vitz. He's equipped with a backpack, patrol droid, commander pauldron, macrobinoculars, T-21B blaster for long range and an SE-14C, with holster, for close quarters. As a Squad Commander, his role is to direct fire, and to order the attack team to engage the enemy. He has no fixed position, sometimes he stays with the defence team, and other times he goes with the attack team.
I added some magnets to the back, in order to attach the backpack. I first cut the backpack flush, only leaving the two small supports for the lower back. Since the backpack is hollow I filled it with hit glue. Then while the glue was still hot, I slathered petroleum jelly over the back of the figure, and made an impression of the back on the backpack. Then I drilled a hole for the magnet on the little "donut" on the back of the figure. The magnet fits perfectly in that circle, however since it's off center, the backpack wouldn't stay in place. So, I added another set of magnets to the lower back. Aesthetically, it's not perfect with the backpack off, but what are you gonna do?
Then I added a holster, from a TIE pilot, and I used a set of magnets to attach the binoculars to the belt. And a set of magnets to connect the T-21B to the backpack. The figure is still new, and the joints and hands are still stiff.