@lightbeam: I have that same problem... sometimes I get to busy to grab some food and all the sudden my stomach starts throwing a fit and refuses any kind of snack. And when "that time" comes around it can suck to actually go out and DO any sort of activity, even if you feel way better afterwards....
Lately I've been having a nectarine or some other kind of fruit for breakfast, normally something with a bit of carbs in it for lunch to get me fired up for a workout (@ Nikki: haha, I had a PB & J today too =] ), and have my protein for the day around dinner which helps me sleep well and keeps my body from getting mad at me XD.
I have to say I am REALLY bad about snacking when I really don't need to (I tend to eat when I'm bored) but I've been working really hard on going for a short walk if I get that sudden urge and it seems to be working so far.