In addition to valuable and irreplacable items, in my opinion it's always a smart and self-protective idea to pack all the items you'll need for the first 24 hours of your vacation. Why? Just in case the airline delays your luggage.
Think of it as a free insurance policy. If your luggage is delayed (delays of several hours up to 24 hours are MUCH more common than actual LOSSES of luggage), then this insurance policy will pay off quite nicely. You'll have with you everything you'll need for the first day. This won't stop you from worrying and/or being annoyed at the delay, but it will help you start your vacation without any actual inconveniences, hassles or expenses.
I mean, I've read posts from people complaining that they didn't have formula and diapers for their kids, or didn't have medications, or didn't have the clothes they needed to change into for dinner 30 minutes after arrival, etc. Luggage delays aren't the norm, I've had it happen to me only twice in the 70 or 80 flights I've taken, but it is a possibility. Why not protect yourself in case it happens to you?
Supplies for the first 24 hours might sound like a lot, but it really takes up very little space, especially when traveling to a warm weather climate. Try it now. Put together a complete change of clothes, one bathing suit (and whatever else you'd need at the pool), toiletries, medications, one set of PJs, etc. That makes a very small mass of stuff, espcially for the kids!
Anyway, that's just my advice. It always makes me feel good to know that in case my bags are delayed, I won't really be inconvenienced.