It's time to start thinking about the garden. In January, I start saving all of my milk jugs so I can use them to start seeds in at the end of February. You can save any size jug. I like the gallon ones because they hold more seeds, but I've used 1/2 gallon and quart sized ones, too - especially for starting onions.
Just rinse the jugs out well and toss them in a box until you're ready to cut them up for seed starters. You don't need to save the lids.