One thing I've noticed as I've been talking to people about P90X is that many people are unsure of what equipment is really necessary for this program. There are a few things offered by BeachBody as you go through the purchase process for P90X as well as other products in the BeachBody catalog. They're all good products but, do you need them? The answer is, maybe. It depends on what equipment you already have, what kind of equipment you prefer, and how willing you are to go out and find things on your own.
I'll run through the list of items you need, then I'll go into detail on those items as well as some optional ones. You need: dumbbells or resistance bands; a yoga mat; a chin-up bar or a way to securely anchor a resistance band at least as high as the top of a doorway; a sturdy but light weight chair; digital food scale; measuring cups.
Do you prefer resistance bands or dumbbells? The bottom line is that the weight training routines require some form of resistance. The kind you choose is a matter of preference. BeachBody offers a couple of sets of resistance bands, one of which is featured in the P90X workouts. If you prefer dumbbells, BeachBody recommends the Bowflex Select Tech dumbbells. It's a good looking design and great option if you're tight on space. If you decide to go with traditional dumbbells, you'll need to make sure you have a suitable range of weights for all the different exercises and you may want to invest in some type of dumbbell rack if you go this route.
I believe the chin-up bar is worth buying. You can simulate chin-ups with resistance bands. However, if you really want to challenge yourself and work up to doing actual, unassisted chin-ups then get the bar. I have the BeachBody bar and it's a perfect for P90X. It has all the grips you need for the program and more. When you're done using it you can take it down and get it out of the way. Even if you feel like chin-ups are way beyond your fitness level, as you progress with the program and especially if you do more than one round you will definitely get to a point where you will want a chin-up bar. They show you in the workouts how to do assisted chin-ups with a chair. Even the assisted version is challenging enough that you cannot fully simulate it with bands.
Another product featured in P90X is the "PowerStands". These are used for push-ups. The benefit is that they make push-ups a little easier on your wrists. The PowerStands are in a fixed position unlike some other pushup bars on the market which swivel. I think either kind will work great. If you don't have wrist issues then you don't need them. If you do have wrist issues or if you just think you'd just like using the bars then the thing to consider is whether you want the freedom of movement from the swivel action or the greater stability of the stationary version.
Whether you buy it from BeachBody or elsewhere you will want to get a yoga mat. You may also want to buy a second mat that offers a little more padding (for the abs routine), depending on the type of surface you will be working out on.
A heart rate monitor is a valuable tool, especially for the Plyometrics workout. I highly recommend having a heart rate monitor. It's not absolutely necessary but, it really is a good idea when you're pushing yourself as hard as you do in this program. BeachBody offers a Bowflex heart rate monitor that does not require a chest strap. Polar is another quality brand that makes several models of heart rate monitors. Most if not all of the Polar monitors do require a chest strap.
Various exercises throughout the workouts will call for a chair. A few things that require a chair are seated exercises, assisted chin-ups, and dips. You'll want to find a stable, firm chair that can be easily moved around, that you don't mind putting your feet on and that allows your hands to be wide enough for the triceps dips.
Last but not least, since I know you will be following the nutrition plan, you'll need a few things in the kitchen. Besides the usual pots and pans you'll need a digital food scale and measuring cups to keep track of your portion sizes. A blender or some kind of shaker is nice to have for protein shakes.
This may seem like a lot to add on to your P90X purchase. Remember that some items are optional. Also, keep in mind that it's an initial investment that will actually save you money in the long run and all the equipment you buy for P90X can be used with other fitness programs later on.