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.
Homemade bread. Nothing beats the smell of fresh bread. Just took a loaf of shokupan out of my oven and the smell in my apartment is incredible.
Learn to make it yourself my dudes, it is 1000% worth it.