Another option that my 2 and 4 year olds love is the little backpacks by Sassafras. They also have roller wheels. My daughters look so cute pulling their 'wheelies' through the airport.

http://www.sassafrasenterprises.com/product.asp?lt=d&deptid=5677&sec=kids&pfid=SAS00030

You should also check out the adorable toddler and big kid backpacks by Dante Beatrix - I got them for all three of my children and they're great. The Dante Beatrix Eco Backpack is made from recycled plastic bottles - very cool. You can find them at IttyBittyLadybug.com.

http://www.ittybittyladybug.com/catalog.php?category=52

does anyone have experience with the trunki?

We travelled a ridiculous amount when I was a kid and as it was just my mum and us three kids she had very firm rules about packing. From the time we could hold a bag the rule was 'if you can't carry it then you can't bring it'. At 3 or 4 years old this applied to toys but from the time we were about 5 or 6 it applied to everything. Needless to say we all have the ability to travel light.