Ummm.. I'm so glad you asked this question. I was registering and thinking.. HOLY MOLY I HARDLY REMEMBER. It's been 6 years since I was last pregnant so I kinda get that I don't remember much... But I do/did remember some.
Things I found unnecessary:
Don't register for blankets unless there is a particular one your really want
Pack and Play (with the changing table thingy attached)
Depending on house size- Monitor
Bottles (I BFed and pumped)
Bottle cleaner thing
I loved the space saver high chair thing but I registered for a real one this time
LOTS OF DIAPER RASH OINTMENT
Humidifiers are good to have
Binkies (Pacifiers)- I registered for multiple because DS really took to one type and didn't like the others
Baby Bath with multiple stages
Baby Bjorn - I always wore DS around while doing stuff around the house if he was awake!
As for registering of "generic" stuff. I registered for just plain onsies long and short sleeve. That Might work to tell people you want them but they don't have to be anything in particular.
ALSO- I registered for TONS of Diapers.
I agree! I didn't find out gender in past so never registered for clothes! I found people bought clothes after the baby was born despite having bought a gift prior. Clothes are hard to register for as they may not be available around time of shower. I loved my baby K'Tan. I agree with a baby bath tub. I wouldn't recommend registering for a bunch of older baby stuff unless you have tons of space to store it. I personally didn't register for anything related to pumping or breast feeding as I prefered to buy my own....I'm weird like that.