Put the sugary cans in a plastic tub inside the cooler.
For example:
A huge benefit to this method is that the person doesn't have to feel the cans one by one. Just find the tub. You need to use an appropriate shape to reduce the risk of cans rolling in or out.
You can stick a label onto the top/side of the tub to remind others not to put other drinks in it.
or
Use a different sized can
A standard treatment for low blood sugar is typically around 15g of carbs whereas a standard soft drink (soda) can has around 38g. In Australia we have multiple can sizes including 200mL which has about 20g of carbs. That works well for me. If smaller cans are available where you are, you could ensure they are exclusively full-sugar.
This depends, of course, on what protocol the person uses for treating hypoglycæmia.
or
Use rubber wristbands
They don't need to have anything written on them. They're just prettier than rubber bands or duct tape. You could also put a message on them (the person's name perhaps) to stop them being drunk by others.