Collect worn-out socks and underwear throughout the year. When traveling, wear and toss. You'll lighten the load and make room for souvenirs as you go. Investigate packing organizers. Pack clothing, socks, underwear and personal items in zipper food storage bags to cut wrinkles, protect clothing, and organize suitcases.
Commercial organizers can be worth the cost for frequent travelers.
For easiest travel with kids, use large zipper food storage bags to pack a complete outfit for a single day. Dirty clothing can be re-stored in the bags. Plan for T-shirts. Deliberately under-pack, knowing you'll add these garments along the way. Put together personal care kits for each family member in a zipper bag or cosmetics organizer.