Update: my sister wrapped my birthday gift in a cereal box and I didn't open it for 6 weeks
I finally opened the Cheerios box she handed me at my party in March and it was a $5 gas card, so I asked her why and she said 'you always say gifts should be useful' and honestly she might be a genius.
My take on gift giving has always been that the thought matters more than the thing, so a cereal box trick would have bugged me a year ago. Reading this, though, I get why she did it. A gas card beats some random candle I would shove in a drawer and forget about. The delay part is weird but kind of funny, since you sat on it for six weeks and she still came out looking smart. Honestly the useful rule is a good one and I might steal it for my own family this year.