Use the screwdriver on the digital lock of the drawer in Joe's house, the code is 7542, but you don't need to use the screwdriver
For the code to the safe at the grandmother's house, look at the bottom-left of the card under it (By the phone). The number is different every time. The safe has washing powder that you give to the europa pizza guy for his flag (Solution to that further down this comment)
To make the flag, get the white cloth by the left side of the left grave inside the graveyard, and mix the cloth with the sauce
To get the sauce, use the jar you got with the fireflies to the left of the graveyard entrance and give it to the guy at the cake shop. Get the money for the cake under the cushion of the chair at the grandmother's house
To make the blue cheese, mix mold with the cheese on the counter, the mold is on the grave where you get the bucket, the grave on the far right (The answer to the puzzle is the name)
To unlock the safe in the europa pizza kitchen, look at the flags on the front (black, red, yellow, blue, black, white, red, white, red)
To unlock the door in europa pizza kitchen, go to the grandmother's house and look at their phone number by her fridge. It's different every time