Unfortunately, laptop and external drives are best
At least, that is my opinion. The problem with any of the self-contained image storage units is that the transfer rate is generally slower and a single unit provides no redundancy. So now you have to buy two devices and that starts getting expensive.
The trade off, of course, is weight and size. I generally carry my laptop (Lenovo T61) and two 2.5" external, USB drives (Western Digital Passports). I put the images on one external drive and backup to the other. The big advantage, besides redundancy and speed, is the ability to run Lightroom and get some editing done. I can also email images while on the road, if I have Internet connectivity.