Here are some of my ideas:

Rope:
9 string crafts a rope
Rope can be hung on a ceiling block and will drop down towards the ground. (Ex: 10 blocks max)
Rope can be used like a ladder
-Player walks up to rope- -Starts going upwards like the were climbing a ladder-
This will allow for a way to use something like a ladder, without having to place it on a wall
The player could make cool parkour challenges using the ropes.

But what could rope be crafted into?

How about....

Grappling hook:
Crafted by:
Iron in Middle row (left and right) and Bottom row (center)
Rope in top row ( Left or Right)

I, as a player, have always hated making ugly 1 block towers to get up to a certain point.
They are an eyesore and a pain to take down.
What a grappling hook would do is:
The player would throw it and whatever block it touches, it would let down a climbable rope. Then to pick it back up to player simply breaks it.

Another cool Idea that rope could be used as a crafting material..

Rope dart:
Crafted by:
Rope + Sword of your choice (Stronger Sword makes a more powerful dart)
This would be a really neat idea. In other games like "Assassin's Creed 3" or "Mortal Kombat" the player have always had fun using these.
It would work like hooking a mob or player with a fishing rod.
The player would right click and it would cast the rope dart.
When it hits something it sticks in it.
The player then right clicks again to retrieve it.
When it hits a mob or player it would deal the damage that the sword used to build it would deal
Then it would pull the mob or player towards the caster when they retrieve the dart.

I think rope would be an amazing addition to minecraft.
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Another Addition That would be useful would be....

Linking minecarts.

I have always wanted to make an actual train in minecraft.

To craft:
for 2 linked mine carts: Mine cart + Iron + Mine cart
for 3 linked mine carts: Linked mine carts + Iron + Mine cart
and so on

When linked the the minecarts will operate as one.
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I also have some food item ideas

Burger:
Top- Bread Center- Cooked Beef Bottom - Bread
Replenishes 10 Hunger Bars

Sandwich:
Top- Bread Center- Cooked Pork Bottom - Bread
Replenishes 10 Hunger Bars

Taco:
Top Row- Wheat (Left and Right) Cooked Beef (Center)
Middle Row - Wheat (Left and Right) Cooked Beef (Center)
Bottom Row- Wheat (All)
Replenishes 10 Hunger Bars