I've got the T-shirt, too. Complete with food stains.

I've always made no-cook lunches SOP for just that reason (and the fact that it's more convenient.) After all, it's not just weather that can screw up the meal plans. I've occasionally reached the planned campsite at 2pm, decided it was too soon to stop for the day, and ended up at a dry camp when I did stop. Usually, I'll carry water from the last source I come to during the day - but sometimes I don't realize that it was the last source until later.

I've also ended up, during a drought, arriving at a planned campsite near dark only to find that the "perennial" stream had dried up.

Net effect: I didn't have enough water with me to cook supper. So, the next day's no-cook lunch became supper, and the next day I arranged to stop (or carry extra water) and cook lunch.