In terms of what you need for the actual pool itself, you'll need a liner, a hose and tap adapter, and then some way to get the water back out after the birth, some people use buckets, but I'd recommend a submersible pump. I would get the liner and submersible pump from the company you hire the pool from, unless you know you can get the same pump for less than the hire cost elsewhere. You want to make sure whatever you have fits your pool and works well with it and I think the company is probably the best place to at least get this information, even if you don't buy from them (but to save yourself the hassle, if the cost isn't much different, I'd probably buy direct from them). We just used our regular garden hose to fill up the pool (ideally clean and soak in sterilising solution in advance), though some pool companies do sell food grade hoses for you to you. I didn't personally feel like I needed one of those. The tap adapter will need to be specific to your tap, so I'd take some pictures to your local hardware store and ask them to recommend something.
That's really what you need for the pool itself. You'll also want some waterproof floor coverings (some shower curtains or a few plastic tarps) to cover your floor, around the pool, but also extra for after the birth when you get out and if you decide you don't want to birth in the pool. I actually only stayed in the pool for 20 minutes before I got out because I didn't like it. Unfortunately, all my floor coverings went under and around the pool and no one could get them out because of the weight of the pool. Having extra would have been a good idea. Then just all the usual things you'd have for a home birth, towels, snacks, drinks, music, candles, whatever it is that makes you feel comfortable and relaxed. But you really only need the very basics from your pool hire company, which they should be able to supply, but you don't need a fancy package, if that's what they are offering.
