A packet of GU provides just that. The entire serving will be delivered to your gut in less than 10 seconds. Hundred-calorie packets make for ease of tracking calories as well. Gel companies that entered the market at a later date simply adopted the 100-calorie portion size. Sure, just check out the pharmaceutical industry.
Several things influence the life of a gel.
This lengthens its shelf life. However, flavor does change with time. Plastic is porous. Flavor will change, and the effectiveness of the ingredients will diminish. If you don't use it in a few weeks, throw it out.