Mine is lilacs, because there was a lilac bush at the bus stop that I used to wait at with my mom when I was a kid, it was my school bus stop and the public bus stop so we spent a lot of time on that corner and now when I smell lilacs I just immediately feel like a kid again.
A core memory unlock scent for me is any time I smell honeysuckle. We had some where I grew up, and it just instantly takes me back.
Others are a spray from Lush called sleepy time. It’s Lavender and Tonka, and it is the most calming scent I’ve ever been around.
Dark chocolate. Good roasted coffee. Wife’s body spray Tea and Bergamont from bath and bodyworks.
My weird ones are lumber and gasoline