In an interesting way the smell of something can conjure up both good and bad memories. There are smells that I love: freshly sharpened wood pencils, inside binding of a new magazine, cut grass, and then those that invoke memories, like Herbal Essence shampoo and french fries.
My best girlfriend in junior high had thick black hair that hung perfectly down the middle of her back. She always used the same shampoo and cream rinse and when she walked by, you could smell the aroma of Herbal Essence shampoo.
My mother never considered the ramifications of dinners including a plate full of fresh fried french fries loaded with salt and ketsup. Moderation is key. It wasn't an every day occurrence, and it was a total treat.
To this day, every time I smell those two things, memories of junior high, or sitting on the counter smelling the hot grease cooking on the stove next to me, instantly send me back to that time. I love it.
I'm sure that there are many smells that invoke memories for you too.
Name a few.