Having lost a mother to cancer not too long ago, one of the things that seems to have a meaningful impact for at least me, is having some of the physical items that feature in some of the pictures and videos. As stated elsewhere, while those images are powerful, and great at capturing some of the "essence" of a person, there's something even more that comes from seeing that person with an object - figurine, painting, sweater, necklace, chair, whatever - and then being able to touch that actual object today. It lends a physical manifestation to something no longer physically here. The picture/video puts it in context, but the object itself makes it "real" in a way that just looking at the pictures doesn't really do. Also as stated by others, there's the earlier periods of time to consider as well - don't focus all on the "now that we know our days together are numbered" moments to capture. Go back and look at the photos/video/records you have from a better time - talk through some of those and capture what you can as well.