Cash

I don't think it matters, as long as you keep track of what happens to it from your cash book.
What I did was a 'private transfer'... (read: you put it in your private purse), so;
1st line: DATE | DESCRIPTION OF WHAT YOU RECEIVED IT FOR | +xxx.xx euro
2nd line: DATE | Private transfer OR Bank deposit | -xxx.xx euro

At the end of the month, this balance will be 0 euro.You can also choose not to do this, in which case your closing balance (and opening balance for the next month) will state xxx.xx euros.
Then you are essentially your own bank.