Pack half of what you’re bringing on vacation in your luggage, and the other half in the luggage of your travel partner. And, your partner should do the same: half of his stuff in his bag, half in yours. That way, if one bag gets lost or delayed, it won’t ruin your vacation.
When you arrive at your destination, no matter whose bag is lost, you’ll each have at least enough to get by for the first few days. When you’re gambling on whether or not an airline will misplace your bags, it’s best to play it safe–this way, a lost bag is just a delay, not a vacation stopper.