Hindsight is always 20/20! I've lived though the 90's and looking back, there were many opportunities but the opportunities were not obvious at the time.
I had the opportunities to register domain names for free, but at the time, there were no websites, no HTML, no HTTP. We were connecting servers via dial-up modem and connecting FTP via IP addresses. At first, I was told to only get the names that matches my business (if I had one), then when Network Solutions started to charge $35 per domain per year. I didn't get into domaining until later, but I still made some money.
In the 90's I've also bought Apple and Amazon stocks. But I didn't keep them at the time because Apple was not doing well and Amazon was just an online books and CD seller. I didn't get into stocks until years later.
I wished I have gotten into Bitcoins 5 years ago. At the time a Bitcoin was already at $500, but it was mainly used on SilkRoads which was just shutdown by the feds.
There were many missed opportunities, but there will be plenty of opportunities to come.