Clips to hold the 'secure lid' in place when your snake begins to test its surroundings. Snakes are exscape artists, and BP's are no exception. Snakes have the uncanny ability finding weak points, and from my experience, they remember where exactly they exscaped the first time, thus they're out again!
It's entirely up to you, but I've discontinued glass enclosures. They do little for ball pythons especially, in the way of keeping their needs met. Glass terria do not hold heat, nor humidity levels well at all, which you will find out sure enough.
Both my ball pythons are housed seperatly; one is in a sterlight, drilled holes on the sides (for ventilation) and for stacking ability. The other python is being housed in a Vision.
Both cages are heated using UTH's (heat tape), hooked to thermostats, and timers, comeplete with digital thermometers. The heat tape is hooked to the thermostat, and the thermostat is hooked to a 24 hour timer, set to run for ten hours in the summer months. So, from 7 AM to 5 PM, the heat source is on. At 5 PM, the timer automatically cuts off all heat in the cages, or basically turns everything off for me. This way I don't have to manually turn buttons off/on and I have a nice steady temperature gradient year around, unless of course I'm cycling my pair.
Just something else to think about. Glass terria are not the only options to house snakes, and if you do your homework well enough, you'll find many keepers do similar setups like myself, or even rack systems.
By the way, since no one mentioned it, day temps - 88-95F (basking), 78-82(cool end). Night temps - 78-80F (warm side), 74-78F (cool side). Humidity levels - 60-75% but I perfer 60% myself.
Good luck, and I can't stress enough, read, read, read.
These snakes are long lived in captivity, and keep asking questions because you'll get a pethera of opinions and advice.