Here is a contraption that is easy to build but difficult to get the materials for (if you are playing in Survival mode). You will need any amount of Redstone, a Sticky Piston. You will also need a redstone signal source such as a Lever or Button. Don’t forget a Block of Slime.
Instructions:
1: Place the sticky piston facing upwards; then place the slime block on top.
2: Place the redstone source next to the piston or connect the source to the piston with redstone dust.
Now to try it out! Stand on the slime block, activate the source, and you will be bounced up 7 blocks or more as long as nothing is blocking you. This machine also works on many entities such as minecarts, armor stands, pigs, zombies, and even items!
PS: Don’t try to bounce a block though; it will stick to the slime block!