Buy glucose in flat rectangular blocks. I find it in the sport supplement section of the supermarket, not the pharmaceutical aisle.
Wrap in a small amount of plastic wrap. I wrap one single, and two end to end.
Three 3g blocks fit longitudinally in a credit card slot of a standard leather tri-fold wallet.
You can see a faint bulge at the right hand edge. As the glucose does not overlie the bulk of the cards it only increases the thickness of the wallet by about 1mm. Having 3 teenagers means my wallet is never too fat from banknotes.
If 9g is not enough of an emergency supply for an average day, you really ought to re-think your diabetes management.
Addit. For watersports, use waterproof adhesive tape to form a loop at the base of a gel packet. Tie it to the waist string of your swimmers or anywhere else convenient. This way you can even carb up under water.
For skiing, mountaineering etc wear the gel as a necklace. You can take on carbs using only one hand and without taking off your gloves/mittens by biting off the gel top. Please also tape the gel top to the body so that the gel top doesn't become litter on the ski track.