SOLVED. main character had a box that s/he could not open until some age/time that was given by his/her father [s]

[Roger]

And when s/he opens it s/he finds a colletion of rocks that his/her father kept as memories of certain events. (his/her father is dead) Also, main character's friend collects playing cards and completes his/her collection (deck) with the last card provided by the main chracter's dad.

[Jessica (Goldenfurpro)]

This is definitely Jeremy Fink and the Meaning of Life

[Roger]

Yes! This is it. Thank you so much!