I keep a few different things around.
In the front of the car I have a pack of dextros tabs, in the boot I have a plastic sandwich box with a couple of cartons of orange juice and a few cereal bars.
Most of the time I carry a handful of jelly babies in a sandwich bag. The do get a bit squashed but at least they don't crumble like the dextros do. My handbag usually has a frusli bar, they do get squashed but again they don't crumble as much as the crispy cereal bars.
At home there are usually jelly babies, or similar sweets in the kitchen cupboard and packets for the dextrose tablets in the medicine cupboard, my bedside table and a few other places. If we have orange juice in I will drink that.
I really don;t like the taste but I do keep a bottle of lucozade type drink in one of the low cupboards. Unlike the orange juice it won't get used for anything else and it's what the kids have been told to bring me if they think "mummy is being strange".