I second using zip lock bags. I packed all DSs clothes in gallon sized, separating out complete outfits for each day, underwear and all. For DH and myself, I got the 2.5 gallon bags and did the same thing. If you roll your clothes, instead of just folding them, and then use a straw and suck the extra air out of the bags, these are just as good and better than the luggage travel space bags. Then also, you can designate bags for extras, one bag for extra socks, extra underwear, etc. It makes packing and unpacking a lot easier. It also makes mixing up the luggage easier, meaning, you want to make sure that everyone has a least one outfit in each piece of luggage incase anything happens to any one bag of luggage. That way everyone has clothes if only one bag makes it to your destination in a timely fashion.
The luggage sized travel space bags are relatively small, and don't hold much. The bigger space bags require a vaccuum to get the extra air out.
Happy traveling!