Importance of Receipts

After my long vacation (Wednesday - Sunday) I am realizing the importance of receipts. I am having trouble calculating what I actually spent this week because I failed to keep all of my receipts. While I can go back and check my bank statement for most of the expenses, that money in my wallet (that is now mysteriously gone) cannot be totally allocated a particular expense. Once I have the time to rack my brain a little and determine where the money went, I will confess to all of my spending.

How do you keep a tally on all the cash money that leaves your wallet?

Following a particular budget is rather challenging. I thought that it was going to be easy, but boy was a WRONG. Each month I find myself going over in a different category. Where is the balance? This month, I am definitely feeling the gas prices. And still wanting that stimulus check. How can I stimulate the economy if the government doesn't give me my money?