Petty Cash
The best way to manage Petty Cash is to treat it like another bank account. In that way when you draw money from your bank account to fund petty cash you can perform a Bank Transfer and when you spend money from Petty Cash you can simply select it from the Bank Account drop down list. To do this you simply create a Bank Account and call it Petty Cash by accessing Settings (or Money), Bank Accounts, Add Account from the main navigation menu. Simply give it a 0 account number and whatever initial balance is currently contained within it, then perform a Bank Transfer for any money transferred into it to
Handled in this manner it will appear on your Balance Sheet and you can easily keep track on incoming and outgoing amounts and can even carry out a Bank Reconciliation on it if required.