The Loot Cart returns to your village after any defense, returning part of the resources that were raided off you. Note: you can never have more than one Loot Cart in your village at a time.
This means that if you leave your Loot Cart uncollected, go offline and get attacked, the next time you log on, you won’t have two Loot Carts. You must collect that first Cart in order for another one to spawn in its place.
If you collect your Loot Cart, go offline and get attacked twice, you will return to find one Loot Cart. That Loot Cart will present part of the resources stolen, calculating the amount from those two attacks.