I've been stringing wires around behind the panel, and experimenting with ways to keep the wire bundles organized as I build them up one wire at a time. A lot of folks do this with tie wraps, but that seems like it could be very wasteful – especially if you're freaky about keeping your wires neat like I am. Every time you need to add another wire to a bundle, you have to clip off the old tie wraps, throw them away, and install another set.
I tried masking tape instead of tie wraps, but I was almost immediately annoyed by how fiddly it was to peel the tape off the wire bundles. So, time for a new idea.
I've had this box, which contains several yards of self-adhesive velcro, laying around my shop for years. I cut out some small pieces and stuck them to each other, so I ended up with a handful of velcro strips with hooks on one side and loops on the other.
These velcro strips can be temporarily wrapped around a wire bundle to keep it from unravelling, and of course being velcro they come off without fuss.
Another way to temporarily keep wire bundles tidy is to use twist ties. I made a bunch out of three-inch lengths of some solid-core copper wire I had laying around. The red insulation will help me remember to eventually replace them with actual tie wraps when I'm finished running wires.
As you can see, this helps keep the wires together in neat bundles (but I'm not wasting a pile of tie wraps).
You can even run the wire ties through one of those little nylon tie wrap anchors I love so much:
I've found that I tend to use both methods in conjunction – velcro strips to hold things when I'm pulling a new wire and I just need an extra hand, and twist ties when I'm through adding a wire to a bundle.