I have the book of maps of the city I live in, which lives in the glove box. If I am travelling, I tend to put the map for that area in as well (I have lots of folding maps of most areas I travel to relatively frequently within the country - as I do a bit of hiking with Cubs and family).
I try to keep at least 1 bottle of water - at the moment, I have a 6 pack of 1l sportscap bottles.
I almost always have a roll of wine gums or chewy mints or similar.
And generally there are a couple of bars of chocolate or nature valley bars (as DD gets into the car starving and I want to avoid meltdowns on the way home).
A travel pack of tissues in my doorwell, along with a couple of pens, handcream, a nail file and an asthma inhaler (mine). There's usually a Sudoku book there as well, for when I'm waiting for DD to emerge from places...
A USB charging thing to go into the cigarette lighter socket and a USB cable for my phone.
Reusable shopping bags, including a couple of insulated bags.
A dry bag containing a pair of oilies and a warm gilet.
I think I have a swiss army knife (basic) in the glove box.
I definitely have a small toolbox in the boot, which has gardening gloves (protection if I need to change tyre or anything), a couple of cleaning cloths, a couple of re-chargeable handwarmers, a decent torch, more pocket packs of tissues, some nappy sacks (as bin bags), a Ziploc bag with basic first aid supplies (antiseptic wipes, bandaids, latex gloves, and 1 battle-field dressing) and a couple of treatsized bags of haribo.
I keep meaning to add a couple of tools to that - a flat head and phillips head screwdriver, decent knife, adjustable spanner. And I need a replacement car bin as the old one fell apart.
In winter, I add a warm hat and gloves each for myself and DD to my toolbox, and I intend to add a fleece blanket this year as I have space (I used to have a Mini, now I have a small estate).