Minecraft – How to make it so players can’t destroy farmland by jumping on it

This answer is for 1.12 or before. Refer to this answer by pppery for 1.13 and later.

You can set up some simple commands with command blocks, and let players click the button of each command block so that they receive the enchanted items.

You can use the following command to give players enchanted items (in this example, 1 diamond sword with Smite 2 and Knockback 30)

/give @p diamond_sword 1 0 {ench:[{id:17,lvl:2},{id:19,lvl:30}]}

This is the general command:

/give @p <ID> <amount> 0 {ench:[{id:<0-62>,lvl:<1-32767>},{id:<0-62>,lvl:<1-32767>},...]}

You put all enchantment tags between [ ], each with both id and lvl tags wrapped together by curly braces { }.

You can also add in the clear inventory command to ensure they don't get kits twice.

/clear @p

Remember the highest level for the enchantment is level 32767. You can stack enchants as many times as you want such as:

/give @p diamond_sword 1 0 {ench:[{id:17,lvl:32767},{id:17,lvl:32767}]}

After setting up the command blocks, put buttons and the players can choose by clicking them.

You can also put enchantments onto things that normally cannot be enchanted or have that specific enchantment. For example, you can do the command stated above to give you enchanted blocks. But, enchantments will NOT affect how the thing works normally. For example, enchanting Thorns on a dirt block will not hurt players when they come into contact with the enchanted block.

You should use a dummy variable and target selector arguments.

Run once

Have a dummy score, call it healthDif.

/scoreboard objectives add healthDif dummy

Run every tick, in order

Set each players healthDif score to their own health score:

/execute @a ~ ~ ~ scoreboard players operation @a[c=1] healthDif = @a[c=1] health

Subtract the other player's healthDif score from your own:

/execute @a ~ ~ ~ scoreboard players operation @a[c=1] healthDif -= @a[rm=0] health

Now players with a positive healthDif score will have more health than the other player. Target with @a[score_healthDif=1]
Note this will only work for two players. In order for it to work with more, you have to take a few extra steps.

Run once

First you'll need a dummy variable to store miscellaneous variables. Call it vars. Note: If you already have a variable for this (you likely do), you can skip this step.

/scoreboard objectives add vars dummy

Run every tick, in order

Put these between the two commands from before.

First, set the #nplayers to 0:

/scoreboard players set #nplayers vars -1

Now, have each player increment #nplayers:

/execute @a ~ ~ ~ scoreboard players add #nplayers vars 1

Finally, multiply each players healthDif score by this number

/scoreboard players operation @a healthDif *= #nplayers vars

This way, you can have any amount of players, and the system automatically adapts!