The best high-GI food I have found is Welch's fruit snacks. They are superior to glucose tablets: (1) Can be swallowed whole quickly and easily, or dissolved by saliva. (2) More concentrated, so you can pocket or pack more glucose in less space. (3) Can be compressed in a pocket or backpack without turning to powder that leaks everywhere. A packet of fruit snacks is 17 g of carbohydrate, which is small enough to catch moderate crashes and large enough when doubled to catch major crashes.