I bought the most fantastic portable high chair ever. My husband and I took our 2 kids to Seattle this past summer and I needed something light and portable to take on the plane for my littlest guy. I found at walmart.com a booster seat that folds almost flat and zips up made by Safety 1st. It fit in my suitcase. There is a small valve that inflates it in seconds when you set it up. It also takes about 2 seconds to fold back up. LOVE IT! LOVE IT! It cost about $19.00.
I told 3 other fiends about it and they also got it and love it. I now keep it in the trunk of my car. By the way, it only weighs about 2 pounds. Eddie Bauer also makes a similar one that I saw for sale in BJ's and the price was the same.