Open the inventory window by clicking on a Storage House. Then, click once on the following items. A red triangle will appear in the item's square as each is selected.

Row 1, item 3 (wooden boards) Row 2, item 2 (iron bars) Row 2, item 4 (wine casks) Row 3, item 1 (bread) Row 3, item 5 (cooked meat) Row 4, item 1 (animal hide) Row 4, item 5 (plate mail) Row 5, item 1 (axes) Row 5, item 2 (swords) Row 5, item 3 (lances) Row 5, item 4 (pikes) Row 5, item 5 (long bows)

Then, click on Row 6, item 1 (crossbow) to add 10 of each item to your inventory or on Row 6, item 2 (horses) to complete the current level.