What should I bring with me for a day trip to Northern France?

I'm in year 9, and on July the 13th, I'm going to Northern France. What should I bring with me for a DAY trip to Norther France, and how much money should I bring with me?
Thank you.
10 points for the best answer
Update: Yes, they told us about the EHIC card, so my mum is getting it when she comes home which should be soon. thx :)
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