My mom found this book at the christian bookstore (although I think you could find in anywhere) that was like a diary of her life. It asked a question on each page and she answered it. It asked about her childhood, how she met my dad, what school was like, what her fave memory of her mom and dad was and so on and so forth. They had one for moms and one for dads. It was the coolest thing ever. We got the story of her life for Christmas one year. It took time, but was the cost of the book.
I want to make a cookbook for my older kids as they leave the house with all the favorite and family recipes that they grew up with. One of the things that I don't have is a collection of my mom's recipes, so I can never have that fried chicken again. It's sad. So, I want to give that to my kids.
A book for your son from dad about what every young man needs to know as he grows up. His wisdom all in a book. What he wishes his dad said to him, all the questions that life answered. And then a book from you about what all men need to know from a woman's perspective.
The reverse for your younger daughter.
An opportunity for them to make such a book for their family with coupons for time set aside to work on that book, with the stuff to make the illustrations.
Art supplies in all types of art, from painting, to drawing, chalk, collage, decoupage along with some local art lessons for the youngers.
For the bigger girls, crazy as this sounds, some mix cd's of music that will remind them of home, growing up, the music you listened to, the crappy but sentimental stuff they listened to growing up.
A photo of each of them as a child, blown up and edited in an artsy masterful way, kind of like just their face looking down just a bit in black and white, so that it's them but not dated and not just a family photo. Frame it and it can be for their dorm wall.