After Christmas this year my fiance and I found some teeny tiny perfumes (1/2 oz. stocking stuffers) on clearance so I picked a couple up in anticipation of our honeymoon at CSS in 03/2012. Of course the TSA rules regulate all liquids or gels be in containers of 3.4 oz or less and fit in one 1 qt zip top bag, but our plan is to take some partially used (approved size) containers for items we may rarely need, that way when we use them up we can pitch them out instead of taking a full bottle and bringing home a 1/2 empty bottle!
Many of the stores like Target, Walmart etc have travel sections with small size shampoo, shower gel and such that you might find work as well or better than your partially used bottles depending on how partially used your bottles are when it's time for your trip. I love shopping that isle anyway as it gets me excited for the trip. The other thing you can find in that isle are bottles that you can use to put some shower gel or shampoo or whatever in for travel. Both these are nice because even though your partially used bottles may weigh less they are still a bigger bottle and will take up room in your luggage that you may find precious on the way home when you want to pack those souveniers!