How do you lose items?

[Balex92.puf]

Do i lose the items if i leave them behind?

[Maya-Neko]

You loose them if you're dead, when the contract ends.

You can leave stuff back in the house when leaving and being revived after dying will also prevent item loss

[Noelle]

Don't forget that items marked "consumable" (Crucifix, Salt, Sanity Medicine, and T1/T2 of Igniter, Firelight, Incense) are lost once they've been activated at least once.