These should start up after playing 3 days in a row. After that, simply play each game every day to continue unlocking them. They'll appear in the musem menu. Also note that if you defeat the boss fast enough to get through the ending, you can use the remaining time playing the FULL version of the game!
Unlockable
How to Unlock
Dr. Robotnik's Mean Bean Machine (and Game Gear) Final Puzzle Demos
Play for 7 days
Sonic 1 Final Boss Demo, Sonic 1 Game Gear Final Boss Demo
Play for 3 days straight
Sonic 1, 2, 3, & Knuckles Good Ending Demos
Play for 8 days
Sonic 2 Final Boss Demo, Sonic Laberynth Final Boss Demo
Play for 4 days
Sonic 3 Final Boss Demo, Sonic Drift Final Race Demo
Play for 5 days
Sonic 3D Blast Final Boss Demo, Sonic Blast Final Boss Demo
Make sure that Vectorman 1 and 2 are already unlocked on your game, and that total play time is 12 hours. After fulfilling the conditions you will have to exit the game select menu and re-enter for the game to register the game as unlocked.
Unlockable
How to Unlock
Bare Knuckle
Play Bonanza Bros. at least once, play any game(s) at least 30 times.
Bare Knuckle 2
Play Bare Knuckle at least once, play any game(s) at least 50 times.
Bare Knuckle 3
Play Bare Knuckle 2 at least once, play any game(s) at least 70 times.
Bonanza Bros.
Play Vectorman 2 at least once, play any game(s) at least 20 times.
To unlock the "Hints" text for each game, open a game and keep it open for three hours. You don't have to play the game, just let it run. After three hours, exit out, and when you re-enter the game or check the Hints menu in the Extra area, the hints for that game it will be available.
By achieving low times in Time Attack mode on Sonic CD, you can unlock new modes. Visual mode and Play Music will both appear on the Sonic CD main menu. Time Attack in Special Stages appears in Time Attack mode.
Unlockable
How to Unlock
Play Music
Get a total time of 37' 27" 57 or less
Time Attack in Special Stages
Get a total time of 30' 21" 05 or less. Then press left when on the Time Attack screen.
You can unlock certain pictures in the museum by veiwing other pictures in a sequence. You must unlock the pictures in the sequence before you can perform these tasks. After veiwing the pictures, you will hear an odd sound to confirm that you did it correctly. Exit and then museum renter the musuem. The appropriate picture will be unlocked.
Unlockable
How to Unlock
Museum picture 200
Select pictures 12, 23, 54, 10, 22, 25, 39, and 56 in that order.
Picture 160
Veiw pictures 146, 145, 144, 142, and 143 in that order.
Picture 180
Veiw pictures 162, 163, 164, 166, 170, 172, 174, and 178 in that order.
Picture 220
Veiw pictures 18, 106, 118, 136, 137, 138, 139, and 140 in that order.
Picture 260
Veiw pictures5, 4, 9, 8, 3, 6, 7, and 2 in that order.