The only fuel additive I trust in any fuel system is BG-44K. It works. Safely cleans out everything your gas and exhaust touch. It's about $20 a can at most dealerships and is good to use about every 30k miles or so.
I NEVER use oil additives because I work on my own engines. I've worked on other engines that have used them and that was all the convincing I need. Change your oil on time. Use good oil. I don't use synthetic in my Honda.
Use Honda fluids for your transmissions, but 30w motor oil will work just fine in a pinch on a MT. AT uses Dexron 3. Flush your AT every 30k miles and it will last forever.
Mopar Combustion Chamber Cleaner (MCCC) is the only other solvent worth mentioning IMO. On high mile cars that have lots of carbon in them, this stuff will turn it all to goo and blow it out your tailpipe. It's sprayed into the throttle body while the car's running and breaks down carbon and even engine oil on contact. Nasty stuff. It works. I strongly recommend replacing your o2 sensor, spark plugs, oil (flush it twice) and disconnect your catalytic converter while cleaning the combustion chamber.
I use synthetic Valvoline PS fluid when equipped, and Motul 600 Brake fluid in the brakes and clutch.
STAY AWAY FROM THE ORANGE ANTIFREEZE. It turns to jello if you have ANY green antifreeze in the system. Stick with the green stuff and change it every 6-mo to a year.
On my DSM, I use some exotic mixtures in the transmission, transfer case, and rear LSD differential, but since this is a Honda forum, I'll skip it. My DSM's drivetrain has about $3500 worth of racing mods in it so it requires it. Hondas don't need that kind of crap.