So, add rubber trees in jungle biomes. If it's possible to farm them, then only in jungle biome. Which means you would have a valuable resource possibly far from your base which you would need to protect. Rubber could be used in many things like vehicle tires, a ball, garden hose, tool handles, garbage bin, durable storage containers, liners and seals to make things water or air tight... the list goes on...

rubber!
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Thats nice Idea ;D And I full agree ..