I'd say it really depends how long a gap between CD packets we're talking. The wonderful thing about ketosis is that once you're in it, you don't actually need to eat as regularly as you do when you're eating carby foods. In other words, you won't get that sudden dip where you become ravenously hungry. In fact, there have been times when I've suddenly realised it's 3pm and I haven't actually had a shake all day...
So I'd say, if you realise that you're not going to be able to get back home to have your shakes, then yes, you're probably going to have to think about having a green and white meal (as they used to be known). That is, something like a chicken salad, for example.
But if you're talking about a gap of say 8 hours, there's no real necessity to have something to eat. Your body will manage perfectly well, I promise. Let's face it, it does when you're in bed and asleep, doesn't it? If you can foresee that you will be able to get home to your shake, I'd wait till I got home, rather than risk grabbing something that might kick me out of ketosis.
Just my humble opinion, mind.