During a wi fi battle, your Pokemon can use its held item once. The held item disapears after the Pokemon uses it but the item comes back after the battle has ended.
Pokemon with harvest may reuse used berries. in other words, once the berry is eaten, the holder may get another berry of the same kind the next turn and it can repeat the process.
pokemon with Recycle can reuse its held item in battle by using the move Recycle.
Overall, in wifi battles, all items used in that battle will be restored. But in game, it will not be restored/will be gone.
Sources: Experience, Knowledge, The links I listed