at least one hide on the warm side and at least one hide on the cool side (my bp has 4). The hides must be snug to your bp when it balls up. They like to fit in there tight and snug. too big and they won't feel secure. add a branch or 2 for climbing. mine loves to climb as do many other peoples. there must be something in the cage for your bp to rub on to help shedding. if your humidity is low or sheds or bad add a humid hide on the warm side (or just add it for an additional hide). of course you need a water dish big enough for your bp to soak if it wishes. naturally you need 2 thermometers, heat (from a uth/human heating pad and/or overhead light), substrate and a hygrometer.
also, you'll need to upgrade your cage (probably within a year) so be prepared or just start out with a bigger cage now.
check out the ball python forum here on kingsnake.com
I'd be happy to email you a copy of a caresheet i've started - it's full of all the advice i was given on various forums. many people have said they found it very helpful. email me if you're interested.
You can also see some pics of my bp's setup in my photo album (link is below).

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Check Out My Albums
1.0 Ball Python
"Aragorn"
1.0 Kenyan Sand Boa
"Gimli"
0.1 Australian Cattle Dog/Pointer
"Kira"