How to stop Wasting money when having hunger (saving money for military purpose)

Hello, So I'm about to join the German Military forces (Bundeswehr), I have bought all the essentials. however I have only some money left, I will join on 23 of Feb. but how do i cut down the spendings ? I eat at home the usual, bread and cheese with coffee , but i dont want to send much, as I don't want to ask my parents for money.

(I was working for some years, but I left my job. as I am unable to renew my contract without the Military certificate )