When I was in my training for the Army, I did use caffeine pills - it was a jittery and uncomfortable experience, but I couldn't fill my canteen with coffee, and it's not like we were allowed to swing by a café.

Also when I used to go to conventions, and caffeine is handed out like crazy (because, gamers - so pimping your brand of caffeine is an obvious move, and free shit is good for business) - but it's also kinda "required" in order to get the most out of the experience. Late night parties and concerts and next morning panels, and more! Plus visiting the city!

But it's too much for just a normal day now, and the jitters and sour stomach aren't worth it. Part of the problem is that it's basically delivered all at once whereas I can add a little bit more caffeine throughout the day if I need it via coffee or soda or tea.