Some of these things are:
Thumbnail sketches
Thumbnail sketches
Natural world
Personal experiences
Their imagination
Everyday life
Kingdom Hearts is one of my all time favourite franchises, mainly due to the art style and the nostalgic factor of Disney.
The creator of Kingdom Hearts is Tetsuya Nomura, a Japanese video game director and character designer working for Square Enix. The idea came to him when he was working with Square Enix, he managed to meet the director of Disney in an elevator (Disney and Square Enix were working in the same building at the time). The early development process was a bit rocky, one side wanted a game based on Mickey Mouse, the other wanted a Donald Duck title. Tetsuya wanted a game where the game's story would equally involve EVERY character, they settled on a game mainly about a brand new character and having the already known characters play a big role in the story. When Tetsuya pitched his idea to everyone they were a bit unsure on the direction Tetsuya was going, due to the main character having a chainsaw like sword.
The main character was set to be a young boy wielding an unusual weapon. In the end they settled for a less monkey like person and used a plain and simple human form, they also swapped the chainsaw for a giant key (the key will play a big part in the game's story line).
Pablo Picasso
Picasso went through a phase of using cold colours and made them look slightly depressing. He went through this phase because his friend Carlos Casagemas commited suicide in Paris, as soon as he heard of this news he went into a 3 year long depression and expressed his feelings through his paintings. The 'Blue Period' is home to some of his most famous paintings, but he had alot of trouble selling them at the time.
Salvador Dali's melting clocks painting. This is probably his most famous paintings in his surreal career. Dali was really into surrealism and this painting really shows it off, the fact that clocks dont normally melt and the landscape itself is pretty strange, the objects in the painting seem to have potential to look 3D but they actually look very 2D when you look at them properly. A lot of Dali's paintings came from dreams he had, dreams which were so interesting and surreal he just had to paint them.