Another one for Ziplock bags.
Green painters tape can be a friend, if you are labelling those bags. I find it easier to read any notes I make, than putting them on the bag itself. Plus, it pulls off easily without any damage.
Set the bags on something solid, with sides. Deals with your fear of them slip-sliding away while keeping all together and organized. A plastic bin can work well, as then you also have a lid if you want to set the project aside. Label it with green tape too, for easy ID!