This is one of those pieces of advice that I really wish someone had told me sooner. Say, when we first had kids. Or when I moved into my first apartment.
Transitioning from one kid to two, it was difficult to get supper on the table on time. After sharing experiences with and seeking advice from a number of successful parents (at least, parents who seemed to have an idea of what they were doing), I have the feeling that most of the families around us eat supper around the 5 PM mark. That's also the time that our eldest tends to start getting grumpy, if she doesn't have something to snack on. Unfortunately, 5 PM suppers just aren't doable every day of the week.
When I was a kid, and supper was going to be late, my brothers, sisters and I would automatically start rummaging through the fridge and cupboards, looking for something quick to eat. When I realized that our two-and-a-half (then two) year-old was opening the fridge on her own looking for goodies, solving this problem became a priority.
So, to avoid all the crankiness and cupboard-searching, the solution we've found has been to make sure the 2.5-y.o. has a quicker, easier, healthier way to find food than searching through the fridge. In this case, that is to have some kind of snack food on the living room table. Steamed green beans and edamame are a current favourite. On weekends, it's often easier to cut up half a watermelon, or chop some celery with dip, and leave it out for the day.
I suspect the reason why it works is the same reason that drives her to the fridge in the first place: she's looking for the easiest food she can find. The upside has been that the crankiness is gone. And not just for the kids. We often find ourselves snacking on the same food as the older child, since we're usually hungry at that point as well.
We're still looking for solutions for days where our eldest has activities right after school. We've learned to keep a small zip-lock bag of cashews and raisins in the door handle by her carseat, and to bring a bottle of water with us, both of which help. But we're still looking for healthy eating choices for when we arrive home after 6 or 7 PM, and still need to go through supper and the whole bedtime routine. If you have any suggestions, I'd love to hear them!