If you're using disposable ziplock bags, other single-use plastic bags or you're gladwrapping stuff to store in the fridge or freezer, 

These reusable silicone food pouches take large bunches of greens, fresh or frozen fruit, chopped salad ingredients, chopped veg, meat, leftovers (liquid or solid) - and keep them crunchy and/or fresh for days. Just slide the bar to lock the contents inside.

They won't leak, and because they're clear you can see what food's there to use up, so they help stop waste.