the best way is:
1,
eat sandwiches, because it can give enough energy to you but it is so cheap!
2.
drink water and dont drink the other when eating outside, because although hot
drinks just need a few dollar but water dont need money when eating outside
and it is healthy for you!
3.
make a money usage list on paper or the easiest way - excel
(remember to update it and calculate a revenge of the money you use every day!)