i have two young children (3.5y and 2y) and gave all my baby stuff away because we only intended to have the two. i am now pregnant with my third and have been making a list of the things i really couldnt do without.
motorised baby swing (i had the fisherprice aqaurium) i had two. it was the only thing my second child would go to sleep in. (you can get one for £40 on e-bay)
bumbo - i had two of these as well(to replace the swing later on) £10 on e-bay but you will not need this until 4m+
maxi-cosi car seat (light and easy to fit) i wouldnt recommend you buy one secondhand unless you know where it came from. people have been known to sell them on e-bay after a car accident as they get a new one on the insurance.
baby bjorn active carrier (i went through about 8 different types and this is the best for your back) i just got an as new one from e-bay for £30 inc postage.
carrycot for my buggy (mountain buggy) - having the baby face you makes all the difference.
lambskin footmuff for the buggy, it can be used as a liner in the summer, i didnt give it away as i still use it. cost £36 new from e-bay. its now 3.5yrs old and still looks like new.
tiny love cot mobile - fantastic classical music both my babies loved it.
breastfeeding tops - you can do it in public without people realising. i hate exposing myself and fed on a bench at the norfolk show because she was screaming the place down and i couldnt find the breastfeeding room. literally thousands of people walked past me who didnt notice.