Hi Angelina, I think its a great idea, for both you and your daughters – we lost dad on 17 December and mum started a memory box after his death, I think it would have been a good idea for him to have been involved (he was told there was nothing else to be done 13 November so the time was there but sometimes you just don't want to acknowledge it) as it would have been that bit more special to look back over then, he had a lot of input into his funeral, the songs and stuff and people noticed on the day.
I am thinking about doing something similar with my daughter, she is 4 and is missing her grandad now more than ever, mentioning him every day and getting quite sullen, so hoping something like this might help her too.