Keep light equipment from tipping up from cable weight?

Blue tack on the feet of your light equipment. Available at any hardware store and most groceries. 

I had a very light component in my system once and built a support structure for the cable out of, of all things, Tinker Toys.  I know it sounds bizarre but it did the job!

Double-faced tape on the feet, zip ties (in a range of 'attractive colors'....

I've a couple of items that suffer from the noted, but have been able to tuck them under or behind cables that keep them stable...

...and there's always Blu-Tak....

Gift wrap a brick....

I just put a box of ammo on top.  Heavy and dense, they keep everything in it's place.

A chunk of whatever is lying about wrapped in electrical tape. The tape prevents unwanted scuffing of the equipment.

There are a variety of colors of electrical tape available for those with O.C.D.