Where can I safely store my stuff?
I don't have a house yet in Skyrim. If I leave my junk in a chest in a dungeon, will it remain there indefinitely? Will it disappear at some point?
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Your items are not safe - I believe it takes less than 48 in-game hours until the items disappear. The good part is they allow you to start off with a good amount of space in your inventory to hold everything.
Hope that answers your question.