How to complete FarmVille Collections?

Here is a quick guide as to "How to Complete FarmVille Collections?" 

Gardening Tools

• Gloves are a Common that is found via Gifting
• Trowel is a Common that is found via Plowing
• Cultivator is a Common that is found via Fertilizing
• Twine is a Uncommon that is found via Harvesting Sheep
• Pruning Saw is a Uncommon that is found via Harvesting Trees
• Shears is a Rare that is found via Fertilizing

Country Kitsch

• Needlepoint is a Common that is found via Gifting
• Spigot is a Common that is found via Plowing
• Pocketwatch is a Common that is found via Plowing
• Salt Shaker is a Uncommon that is found via Plowing
• Thimble is a Uncommon that is found via Plowing
• Cow Bell is a Rare that is found via Harvesting Cows

Bugs

• Ladybug is a Common that is found via Fertilizing
• Dragonfly is a Common that is found via Gifting
• Caterpillar is a Common that is found via Harvesting Trees
• Stickbug is a Uncommon that is found via Harvesting Trees
• Beetle is a Uncommon that is found via Fertilizing
• Centipede is a Rare that is found via Plowing

Feathers

• Green Plume is a Common that is found via Gifting
• Hen Feather is a Common that is found via Harvesting Chickens
• Dapple Plume is a Common that is found via Harvesting Ducks
• Red Feather is a Uncommon that is found via Fertilizing
• Banded Quill is a Uncommon that is found via Harvesting Turkeys and Geese
• Blue Feather is a Rare that is found via Harvesting Trees

Source : Official FarmVille Forum Thread
It is also said that when at least one of each (Although you can keep 10 of each at one time) of the items in a set are collected, then you will be able to Trade them In for a reward. The reward can be:

• 250 XPs
• 5,000 Coins
• (and/or) 5 Tanks of Fuel