1. Don't forget to bring some coins to throw into it for good luck.
2. Don't forget to bring some coins which you can throw into it for good luck.
3. Don't forget to bring some coins which you will throw into it for good luck.
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Can we change #1 into #2 or #3? Which one is better, 'can' or 'will'?
2 and 3 are wordy. 1 is better because it has fewer words to say the same thing.
2 states what "you" are able to do.
3 seems to be giving "you" an order!