First goto T.Code:VOV7,Select your order item category.Details.
Check whether it is relevant for delivery or not.
If yes then Goto T.Code:0VLP(Zero VLP),Select yourdelivery item category.
Under Warehouse control and Packing tab,there is check box for Relevant picking.
Check this box.
The same you can do in OVLP also.
Here it is direct check box.
You can use either of them.