The biggest challenge, at least for me, with gardening is preserving the harvest. It makes me sick to think of the amount of food I have let go to waste through not having these skills. Root cellaring is something I am looking at hard as it is a no impact way to store food. It uses the earth to maintain the freshness of the crops stored within.
Bury a 5 gallon bucket and cover it with a straw bale.
Build a root cellar from plastic drums
Make it out of pallets
Pallet wood root cellar
A galvanized trash can. This is basically the same as the barrel one so I am cheating a bit.