I haven't really bought any n64 virtual console games except for "Sin & Punishment"Game saves and save data
Game saving is functional and intact on the Virtual Console for all games which originally had a save feature on their cartridge. Saved games are saved to the Wii Internal Memory and function exactly as the original cartridge did. A game which in its original cartridge form did not have any form of save feature will not have any save game feature on the Virtual Console (though depending on its original system it may have the suspend feature as described below).
Most first-party N64 games used internal cartridge memory for game save data and thus will save properly on the Virtual Console. A select few first-party and nearly all other N64 game cartridges utilized the extra memory capability of the N64 Controller Pak. Saving of data to the Controller Pak is not supported by the Virtual Console, so for those games which used this feature, the save feature will not work properly in the Virtual Console.
An extreme example is that of Mario Kart 64 which uses internal cartridge memory for progress and save game data. Consequently all progress is saved properly (since it was saved to the cartridge itself) but one of the features in Mario Kart 64 (saving ghosts for racing at a later date) will not work since that particular feature utilized the Controller Pak, and the option to copy data to the Controller Pak won't function in those games.