I usually give around $300 per week to my maid to do grocery. She keeps track of the receipts and cash movement. I will ask her once in a while.
It's a good idea from keroppipooh to '比本簿佢 keep, 返黎就 mark 番條落簿比我睇'.
I will do it in a differenct way, I will ask my maid to use her money to buy the grocery, and she has to write down all the $$ in the book and I will reimburse the money to her. She need to show me the receipts as well, if I found she brought something useless, then I will not pay her for that item. I have told her in day one and she agree with this arrangment. I found it is quite good since she won't buy a lot of thing home which I don't know!!