Meteorite Bar is a candy bar manufactured by Candybox. It first appears in Grand Theft Auto IV on the website Flyhighpizzapie.com. It reappears as a food/snack which can be consumed in Grand Theft Auto V and GTA Online.
It can be seen in Street Vendors across Liberty City and stores across San Andreas. It could be based on Snickers, since Candybox is based on Hershey, or Milky Way because of the "gooey core" and space-related name.
Meteorite Dark Chocolate Candy Bar
Their ingame webpage describes that the inside consists of melted dark chocolate and peanuts.