What snacks or bars have low GI and can be eat immediately ?
Nuts and seeds (as long as they are not coated in sugar) have a very low glycemic index.
In general, when looking for snacks/bars, look for options that are high in fat, protein, and fiber, and low in carbs. And for snack/bars that do contain carbs, try to see what the main source of carbs is, and whether or not it has a low or high glycemic index. For example, brown rice syrup has a high GI (\~98), whereas dates have a low GI (\~42).
Perfect bars are low GI because of the fat content but are pretty high calorie and also have to be refrigerated (not sure what you mean by eat immediately)
Meat jerkies are also great for ur requirements as are fruits with fiber.