The demo has files for functions added in later updates, such as the sound effects for wolves, weather and pistons. However, they are not used.
If you dig directly underneath the sign telling you how to open the chest, you can find a chest that contains 22 gunpowder.
If you go to sleep in a bed and skip the night, it will remove that time from your clock, decreasing your play time.
If you have a bucket with you after the demo expires, you can use that bucket to milk a cow despite not being able to interact with anything else.
You can also interact with boats after the demo expires.
If you look hard enough, way out from the spawn point, in a desert, there is a chest with a saddle and other necessities. The chest is blocking a small spring from flowing all the way.
If a player goes left when they reach the PC Gamer sign, they will find a skeleton dungeon.
While mining, if you press "e" then keep mining you will keep mining but your pickaxe will not move until you stop mining.
The "PC Gamer" logo can be mined. It is composed of snow blocks, red wool and black wool.
If you dig straight down at the spawn point, at bedrock level, there is 1 diamond.