Kato Kiyomasa, who suffered immensely at Ulsan Castle

When he went to Japan to build a castle:
1. He built 120 wells inside the castle.
2. He filled gourds inside the castle with oil.
3. He used edible taro stalks for tatami mats...
(He reportedly simmered taro stalks in soybean paste, dried them, and used them both as rope and as emergency rations.)
4. In addition, he planted large quantities of sweet potatoes and potatoes inside the castle.
5. He prepared lunch boxes that could last for several days whenever he went somewhere.
(About 5.4 liters of rice, soybean paste, and 300 mon in coins.)
I wonder why he carried the coins with him.