You do not need a tool to harvest crops but you need a hoe to plant them
Leather is harvested by killing cows.
Use wheat which you can harvest/steal from villages
If you run water over a lava source block you will create obsidian. Mine it with a diamond pickaxe to harvest it.
Put a pumpkin in the crafting table or self crafting
With a shovel
You do not need a tool to harvest crops but you need a hoe to plant them
Leather is harvested by killing cows.
Use wheat which you can harvest/steal from villages
If you run water over a lava source block you will create obsidian. Mine it with a diamond pickaxe to harvest it.
The only way to acquire fire blocks in Minecraft 1.2.x is to use inventory editors.
You cannot harvest plants in creative mode because you have all the resources in your creative inventory! So when you harvest a plant, it just breaks.
Put a pumpkin in the crafting table or self crafting
In order to collect diamonds in Minecraft, you have to have an iron pickaxe, if you are wondering how to get iron, you have to have a cobblestone pickaxe and find the brownish looking ore then mine it. Once you have it, you need to cook it into iron ingots then craft an iron pickaxe then there you have it.
You need a Diamond Pick to harvest obsidian blocks.
You still have to harvest and feed them by hand.
You need to be in survival or hardcore. Just attack the material until it breaks and you pick up the material