Honestly the thing I miss the most is the age before smart phones. Because it's made such a difference in the way people conduct their entire lives now. Everything now revolves around, or goes through a smart phone. Before, it didn't. People nowadays (myself included in this) prefer to divide up a good portion of their experience of life through the use of a phone. You see this when people would rather take a picture or video to post, than simply live in the moment. Or they'd rather text someone else, instead of talking to the person they're eating lunch with. Or Googling a quick answer, rather than actually learn by experience or study. Or fill every slightly dull moment with another check-up on social media. I remember what it was like before all of that. It's hard to explain, but I prefer it the way it was.
I miss a lot of old retail establishments that have long since gone away. I miss the convenience of having a lot of places to physically browse for a variety of goods that you just can't even find anymore in a lot of small towns. I miss record stores, rental stores, department stores, toy stores, electronics stores.
I miss the era when pizza wasn't a fast-food, but a special occasion type of eatery. The cost was about $25 - $30 for a decent sized one, and it was damn delicious. Nowadays, it's an inexpensive and bland fast-food item for the most part. Hardly enjoyable.
I also just miss just being young, naive, and optimistic.