You need it because هُناك means "there is". Without it, the meaning changes to "it's not money". "There is no money" = لَيْسَ هُناكَ نُقود "This is not money" = لَيْسَ نُقود

Several positive versions would be correct, including yours. You could say: هُناك نُقود في شَنْطَتِك في شَنْطَتِك هُناك نُقود في شَنْطَتِك نُقود

In the positive version, هُناك can be omitted because the meaning is clear from في. There is no َلَيْس to make multiple meanings possible.