Download and install the TooManyItems mod from minecraft This will add a list of all items on the right of all inventory screens. Click on any icon to add it to your inventory.
It also works in multiplayer if you have operator powers on the server.
Minecraft 1.8 added a Creative Mode which allows you to spawn (most) items in the inventory screen (as well as fly and not take damage from anything). You can't switch any given single player world between survival, hardcore or creative mode without hacking though.
Chat with our AI personalities
Sorry it's probaly not possible ):
I've seen some people enter it in as /Smite <player> through a command block, although I'm not as sure how to do it in Singleplayer mode.
Yes, this mod is available for singleplayer
There is no way in vanilla Minecraft to change game modes. In order to change your gamemode, you must use mods, such as Singleplayer Commands or Too Many Items, which either one can change it. Happy Crafting!
The only way to spawn herobrine in minecraft is to use mods as you cannot spawn him in vanilla minecraft.