Hi, I'm the person who asked this question last month...one month into the program, I have a few suggestions...
If you get a barbell, make sure it is a good quality barbell with large collars (the screw on thingys that keep the weights on the bar). I got a Gold's gym barbell and the collars are so small it takes extra time to change weights. If possible, get the spring collars for quickest weight changes.
I also recommend getting the Cathe stretchy bands...mine are fine, but they stretch differently than Cathe's bands so I have trouble finding correct form for each exercise.
I don't know if Cathe sells slanted/angled risers for steps, but they're great for turning the step into an incline/decline bench. Here's a link if you don't know what an angled riser is:
http://www.power-systems.com/showproduct.aspx?ProductID=4102&SEName=spri-slanted-riser
You might need a squat rack for security if no one is around to spot you when you lift. If you don't want to buy a squat rack and don't use really heavy weights for squats, then you could use a 20lb weight vest and dumbells.
Also, get dinner plate sized flat paper plates-Cathe does several torture sessions, I mean exercises, using them.
Good luck-You're going to love STS!