Since all my families cars are pre 2000's, I've found quite a bit of oddities. My cougar in particular was the WORST. I'm the 2nd owner. Got my car from a small dealer in middle of summer, and noticed the car had a gross sweet smell especially on hot days. The interior would have been mint, if it wasn't for what appears to have been a cup of coffee being flung from the cup holder at 150 MPH.
The leather seats were in excellent shape, but the carpet from front to rear was covered in brown stains like you wouldn't believe. All the soft touch dash panels have etching marks from the probably extremely hot coffee. Everything in the console area had this brown sticky crust all over it. The inside of the armrest storage was the worst. I thought that rubber pad at the bottom was glued in, but after peeling it off I found quite a lovely amount of dried pooled coffee underneath.
Ended up removing the entire assembly and cleaning it really good.
The carpet took a whole bottle of folex. That stuff works GOOD. The entire interior in the end cleaned up nicely, aside from all the etch marks on the dash panels.
Under the seats was a good game of, 'Put your hand in, see what prize you get out'. Vacuumed up a partially leaking packet of mcdonalds ranch from 2004, a lollipop, weird unlabeled candy, an absurd amount of rusted pennies, and a hoop earring.
Will check behind glove compartment to see what other goodies I get.