I need to create a temporary container (which won't exist in the world) and show it to a player. Looking at this plugin and disassembled code, I came up with this code 

var container = new ItemContainer
{
    entityOwner = player,
    capacity = 1,
    isServer = true,
    allowedContents = ItemContainer.ContentsType.Generic
};
container.GiveUID();

timer.Once(0.5f, () => {
    var loot = player.inventory.loot;
    loot.Clear();
    loot.PositionChecks = false;
    loot.entitySource = player;
    loot.itemSource = null;
    loot.AddContainer(container);
    loot.SendImmediate();
    player.ClientRPCPlayer(null, player, "RPC_OpenLootPanel", "generic");
});​

It seems to be partially working: my inventory opens, "loot" area appears but then it is almost immediately replaced by quick craft. So how do I show it correctly?

Check my hooks :p it calls a hook and if you don't cancel it it closes

Thanks, figured it out. If someone ever needs it, the game seems to be checking if a player is looting themself. So, you need to return non-null in CanLootPlayer