We've actually used everything we bought (other than a few items of clothing in the early days but then we never over bought in that department anyways).
I was pretty frugal with baby things. I made sure I didn't buy tons of toys and gadgets as I knew most of them would go unused. We also knew we would not get much in the way of gifts or clothes for LO so were able to buy only what we wanted, not what other people thought we might want.
Big things we got and used
TummyTub (most days)
Bouncer (been good since 8-9 weeks old)
Breast pump, bought after 5 weeks of BF'ing (I expressed a fair bit on and off but don't atm)
Baby carrier - OH uses this
Moses basket and fitted sheets
Sleeping bags in 1 and 2.5 tog. LO used the 2.5 tog in the early days and is back in it now its cooler. Great buy.
As for the rest, things like bibs I never planned on using till older so have a few waiting to see action when we get onto weaning. Never got things like a steriliser, top and tail bowl, toiletries. We were given some baby toiletries and I promptly gave them away to another mum to be.
There really isn't anything we got we've not used. I think it paid us to really look carefully at how we live and what we wanted for our baby and how to achieve it with the least fuss and expense.