I use glucose tabs, exclusively. I keep a roll of 10 tabs with me at all times. If I'm low and the brain is fuzzy, I can eat enough tabs to bring my blood glucose levels back up (2-4 tabs usually are enough to do the trick). And if I'm really fuzzy, I can always count my remaining tabs once I've gotten my BG levels up. For example, if I've got 3 tabs left in the roll, then I know I've eaten 7 tabs, or 28 g carbs (7 tabs * 4 g carb/tab).
Like Lila says, Kit Kats are a poor choice for treating a low. Chocolate sugars and fats will be slow to digest, so you'll stay low longer, and you'll want to keep eating b/c your blood is still craving sugars. Once the delayed sugar onset comes along, you'll likely have a ton of it coming down the pipeline. Glucose tabs, smarties, or skittles would all work better for treating lows. Faster sugar release/response to get your BG up quicker.
Cheers and good luck, Mike