I am designing a database for a game and the only option I can see a multiple table solution. Is there an option that I'm not seeing?
You want to store an undefinied number of items in a list, for this you need a new table or cleaner two tables.

you already have the first table called items, each has an item_id.

Then one table holds all the references to the collections, so best case only a new collection_id for every of the collection.

And the important one is the MxN relation table between items and collections, let's call it collection_items, holding in each row one item_id and one collection_id.

If you want to have multiple same items in one collection, and only want to know how many, add a count field.

But if the relations need to be distinguishable, add a row for every relation and an extra collection_item_id.