I travel frequently and have found that the following works really well for me:
1) I take the caps off of my bottles
2) squeeze them if the bottle is plastic to get extra air out
3) and then put a few layers of plastic clingy wrap over the top opening and ribbed section of the bottle; I use Glad "Press and Seal".
4) Then, I screw the tops back on (over the plastic wrap).
5) Finally, I put bottles in big plastic ziplocks.
6) If the bottles are glass, I then bundle in socks and put in my sneakers.
7) One more thing- mentioned in another response, put the plastic baggy somewhere in the middle of your luggage ( not on the top or bottom
Seems a bit excessive, but it works, and I don't have to worry about crap getting all over my clothes!!
I have had things go missing before from my bag- I don't think that there is a good way to really protect. I figure, even with TSA approved locks, how can you really trust the TSA folks? Three of the most important things that I have learned- check your luggage immediately after you get home or to your hotel. A lot of the airlines have regulations that you have to report missing items within 4-6 hours of flight landing. Lastly, anything that you are going to buy of value, put on your credit card so that you can retrieve older receipts if need be. Lastly, try to use the same airline if you travel alot. I had camera equipment taken from my luggage last xmas. I was told by the airline that "they usually don't cover electronic equipment", but yet they covered mine- I can't help but wonder if it's because the airline checked my record with them and found that my fam has spent tons of bucks with them!
). I can easily use one of those measly 4oz bottles on one side of my hair
STLCovergirl, thanks for replying. 
