A bucket of sand to get the tough dirt off :thumbsup:
For real, it's a tough question. If you're into detailing, you'll be looking for high quality shampoos, 2-3 buckets, foam lances, the nines.
If you're not, you'll balk at the soaps and rigs people have when the turtlewax/rain-x shampoo and rubbermaid bucket from autozone does the same job.
If you fall into the first category: Adams, chemical guys, optimum, and countless similar products. Look into wool pads and mitts, and consider a foam lance on a pressure washer. Get some buckets with grit guards. I got hooked on Autogeek, there's a bunch they don't sell, but there's even more they do, and the forum is crazy knowledgable.
If you fall into the second category: Go for something with a carnuba, and is sudsy. Turtle wax and rain-x make good stuff. The mitts on a pole are a great accessory, toss them in the washing machine after every couple washes at least. Any bucket will do, I'd aim for a taller bucket, not to hold more liquid (try to keep the water clean, it's easier to make smaller batches of mix and remake them often) but to keep your feet dry (it sounds dumb but after august it really sucks to have a soggy set of sneakers after a sunday wash session.