Hi! I am a translator, and I need to translate that piece of text:

"When do you open your Christmas presents? Open them only in the privacy of your own family. Do remember do leave the receipts in “by mistake”, then everyone can charge everything the next week." (SHE magazine)

The problem is that I do not understand the last two sentences at all, or speaking more exactly, I cannot catch the meaning of the words "receipts" and "to charge" in that context. I cannot even guess an aproximate meaning, so I ask for help native speakers of English. Please, restate the idea in a different way or explain me what the hell is going on there? :)