Great tips. The one thing we did (not my idea, but I read on it by researching awesome sites like this) was even though we drive all the time, we packed a small emergency duffel bag using one of those vacuum space-saving bags for the clothes. We packed three outfits for everyone (2 adults and a kid) including underwear, socks, the whole nine. Then packed all the toiletries on top of that.
If our suitcasese were lost (even in a car, freak accidents happen), then we'd have enough stuff to last two days AND the clothes were waterproofed. The clothes would be wrinkled as all getup, but it's better than wearing the same clothes or going out and having to buy new ones, right?
We also used the space saver bags in our carry-on in the parks just in case the kid got really wet, spilled something on himself, or had an "accident". We squeezed three full outfits in a single diaper bag.