Happy Meal
1979 had some seriously valuable Happy Meal Toys, and if you happen to know a McDonald’s fan from that time, they might have a pricey toy in hand. Then there are various themes in the early 2000s which became quite valuable, like some Disney Characters, which go for around $300 on eBay.
Furby
The cutely bizarre Furby was a massive hit with kids back in the 90s, with their animated and noisy designs. If you happen to have one that you never bothered to take out the box, someone could easily pay you close to $1000 for it!