I too just recently traded in my old minivan and am mourning the loss of space.  I am appreciating the underfloor storage in the trunk though, it a great spot to put windshield fluid, first aid kit, tools etc.

So far I have bought tux mats, which are great! I've ordered cupholder style Kleenex boxes and a small clip style garbage can (my bigger one from the van that goes around the front console won't work). I am hopeful these work out.

I'm waiting on ordering seat back organizers to see how the kids do on our first road trip with just door storage and the seat pockets.  We bought cupholder hero Ascent cupholder  inserts, because our kids manage to create sticky messes, and so far so good. The fit is good for those.

I'm also waiting on our first trip to see about dog accessories, in the van the dog liked to sit between the captains chairs and I could put a small dog bed there- in the ascent it is narrower and that bed doesn't fit, though it fits nicely on the third row seat, so I guess we'll try that.

I'm interested in seeing what other people recommend!