When you are expecting a baby, it seems like you need EVERYTHING on these numerous lists all over the internet. It is not true, though. There have been things we barely used (like the reclining chair) and things we have used very much. So what has the latter been?
Cloth diapers - we started with Little Lamb pocket diapers when she was one month old and switched to Grovia AIOs when she was about 7 months old. During the night we use Anavy and PUL pants combination. So basically we use cloth diapers 100% of the time when we are at home. At daycare and during trips away from home, she still has single-use diapers. It is a huge difference though - we have bought only 2 packages of diapers during the last 11 months (and about 4 packages during the first month).
Myhummy - this is our little white noise machine to keep the baby sleeping. We have been using it for 9 months on daily basis (so about 14 hours a day). Worth the price, I would say.
Baby monitor with a camera - a gift I got to choose out myself, the baby monitor has been a great tool to be able to keep an eye on the baby. We still use it daily.
Fedde&Kees sleeping bag and tight fit linen - I have written about these products before (link) but they saved our lives after we moved off from swaddling but the baby couldn't still help the windmill arms. We used the sleeping bag for about 5 months and the linen for about 7 months. Bought them second-hand for 80 or 85 euros and resold them for 70 euros. Not a bad deal, I would say.
Baby carriage(s) - we use our Joolz Day daily and our running buggy at least weekly. We carried her in the baby carrier (Tula FTG, still would really recommend one!) lots until she turned 6 months old and started to sleep again when she is put in a baby carriage. After that we have carried her very little, so when we go out, she is in the baby carriage.
Certain baby clothes - I sweat by Joha (merino wool) rompers and pants. She has been wearning size 70 of them since she was 3 months old (yes, they were very big, but still fit somehow) until now! I bought size 80 but they are still a little big. I have a feeling that one could just get 3-5 sets for size 60, 70 and 80 and you would be covered for the first 1,5 year. Much more sustainable than getting 10 of every size from 50 to 80.
Tripp Trapp baby eating chair and bibs with sleeves - from 6 months onwards, she has been using this chair at least 3 times every day. We have 3 bibs with sleeves that are constantly in use, I could really recommend them!