I save ALL of my plastic milk jugs, OJ containers, yogurt cups, soda bottles..... I use them all year long; wintersowing, Spring sowing, rooting, and as swap containers..... I always have a black leaf bag full in my potting shed....

After transplanting my wintersown babies to garden beds, I use the bottoms of the jugs for swap containers and give-aways.

I use paper cups for starting seeds...I can plant the whole thing. I get BIG packs at Costco or Sam's.
If cut correctly, milk jugs make great apple pickers when duct taped to a long pole or broom handle.

I do paper pots for swaps.That way you recycle and also, plant the whole thing. No transplant shock to roots.

I use my plastic containers for swaps and giveaways too.