I am a big fan of setting up the right kits to deal with specific systems. For exterior, Meguiar's has a really good detailing solution. If your budget allows for it, the MT300 polisher for $230 is amazing:
http://www.amazon.com/Meguiars-MT300-Pro-Power-Polisher/dp/B00OTK5JHG/
Compounding, polishing, and waxing are a piece of cake, all for the cost of a couple exterior detailing jobs from a professional. Chemical Guys have some neat stuff; I've been looking into a shampoo system for awhile, but I've found it easier just to get Weathertech full-coverage floor liners & waterproof neoprene Wet Okele seat covers for the front & rear (if your car is already a mess, just pay a professional to do the interior, let it dry out, then slap that stuff on), that way your interior becomes extremely easy to manage because all you have to do is take our the liners & covers, rinse & dry them off, and put them back in...the floors & seats stay totally mint for resale down the road.
Like imported_Irse said though, it depends on what you've got & what you want to do. My friend just picked up an older Porsche with original paint, and I forget what kind of paint it has, but you have to use special cleaners on it or else everything turns yellow or something. Or if you have leather, you probably don't want to use a seatcover (other than maybe a Katzkin setup or something), so interior maintenance products would be more important in that case.
And also as mentioned, how much time & money you want to spend. The MT300 is an amazing, gamechanging tool imo, but $230 is an awful lot of money for simply waxing your car (especially given that Turtle Wax, which comes with a pad, is under ten bucks for a whole tub), unless that's the sort of thing you're into. I happen to really like waxing my cars & making them shine, so it really depends on what your car's setup is, what your goals are, and what your available time, interest, and financial situation is. There are dudes who pay $90k for elite detailing for ultra-high-end cars, so you can go as bananas as you want with this type of stuff :awe: