Getting power to your equipment. Unless you want to live in a forest of extension cords, you'll need one or more power strips. Some cabinets come with power strips built in. If you need to order a power strip, consider which kind will be best for your installation. Rackmount power strips come in versions that mount either vertically or horizontally.
Surge protection is another important issue.
With all the money you have invested in rackmount equipment, you'll certainly want to make sure it's protected. A UPS keeps your equipment from crashing during a brief blackout or brownout and gives you enough time to shut everything down properly in an extended power outage. Managing the cables. Your equipment may look very tidy when it's neatly stacked in a cabinet. But you still have an opportunity to make a mess once you start connecting it all.