Cable ties. They come in nylon which can only be cut off or the Velco kind which are reusable. If a cable is too long either coil it or lay it back along itself and put a cable tie at each end. Oh, before anyone says it. You really shouldn't coil mains cables up if you're running them close to their rated capacity. Given the number of cables you've got you could also consider PVC cable duct, the kind with slots on the side for cable entry would suit. There's also cable tray, it's available in various widths. I've used left over cable tray to make makes some shelves, I should take a photo of it.