Hmmm...
Coal smoke. Not a smell most (if any) of you have smelled, but the apartment buildings of my childhood were heated with coal-fired boilers.
Smelling coal smoke wafting over the border with East Germany took me right back to my childhood.
The garlicky, fishy, oniony, meaty smell of a traditional Jewish deli. Hard to describe, impossible to replicate. Again takes me right back to my childhood. (and still makes me salivate)
Lavender. Several of my old aunties wore lavender and used lavender soap, etc. I still love lavender and wear it on occasion.
The musty, "papery", leathery smell of an old, hand-bound book.
The smell of tempera paints: the sort we used to use in elementary school. They came in little glass bottles of primary colors. Heck the smell of my elementary school, which was built in the 1800s: Floor wax, both for wood in the classrooms, and marble in the hallways and stairs. The smell of chalk. Disinfectant in the bathrooms. Sweat because there was no A/C, (and quite often no heat).
The smell of mimeograph printouts (dittos) when fresh off the machine and handed out for homework.